One big important thing, remain calm and collective, you want to set the example of being calm so yourself. Dogs tend to reflect the energy level of their owners, and the more calm you are, the more calm she will be. Make sure she goes potty before you leave, and exercise her a lot so that she's really tired. The more tired she is, less energy she has to put towards being anxious or being over excited. Try training her to do a few tricks, and give her interactive toys, you want to tire her out mentally as well. I personally like giving my dog her meals in kibble ball dispenser and the like, it increases the mental exercise without adding too many extra treats. Since she is still a puppy, try putting one of your own clothes that you've recently worn in her crate with her, the smell will help comfort her (make sure it's something you don't mind getting dirty if an accident occurs). Also, give her a something a like a frozen kong stuff with yummy treats in her crate too, it'll be very rewarding and make a positive association with the crate. When you leave, act like it's no big deal, don't even bother saying goodbye to her. If you make a show before you leave and give her lots of attention that will rile her up this tends to set up the dog for being anxious; it's like making a big dramatic goodbye that will devastate the dog. Some people like to put on the radio or the TV for their dogs, being stuck in a crate can be boring and the silence lets them know they're all alone. The sounds kinda imitate someone being home, so the dog can be less anxious.
I am not sure what kind of training you do with her, but I'll just give you all the information I can think of, lol. But first off, if you baby her, you have to stop right away. If you coddle her when she's upset or being anxious, stop that too. Attention and love is all good, but it has to be given at the right time. When given at the wrong time, it can unintentionally reward a negative behavior. It's really hard not to comfort a dog when it's being scared or anxious, but it is something that you just cannot do if you want to build her confidence. Give her attention when she being calm, when she's being good, when she is waiting, when she does something right. However don't give her a constant stream of lavishing, dogs can become addicted to that constant affection so it's harder for them to be alone. Try ignoring her once in a while, it's not like you're depriving her, but just take some time for yourself. Play training games with her and build up her tolerance for the crate and being left alone.
1) Make the crate the greatest place to be! If she doesn't like the crate, she will find a way out. Reward her for going into the crate on her own, and reward and praise her when she stays. You can throw treats and stuff into the crate so to encourage her to go in. Feed all her meals in her crate, let her take all her naps in the crate, and etc.
2) The crate doesn't symbolize being alone, don't just put her in there when you're gone. You want her to see that just because she's in the crate doesn't mean you're going to leave. Put her in there when you're home. Make it random, just put her in then take her out. Put the crate in the kitchen and put her in it while you cook. Put her in it while you watch TV. Put her in there while you go to the bathroom, and take her out when you return. Throw a stuff kong in there for a snack, and close her in while she has the snack.
3) Play training games and practice leaving. Put her in the crate and leave the room, then come immediately back. Do this over and over again so it's boring, and she realizes you're coming back. When she doesn't react to you leaving the room, extend the time you're gone gradually. If you want to feed her treats as a reward for being calm when you leave the room and when you return, just drop the treat in the crate but nothing more. You want to be as calm and nonchalant as possible. But do make sure you only reward when she is calm and not being anxious. If she is, you just need to keep repeating coming in and out until she does before extending the time.
4) Make the act of leaving the house mundane and boring. Dogs pick up routines and patterns really well, and sometimes the routine of grabbing your keys and getting ready to go can trigger the anxiety. You want to make these things happen all the time, so she doesn't know when you're leaving or you're just putting on your coat for no reason. Like the the training games, just randomly do your routine, but don't leave. Keep doing it over and over again so it means nothing. Throughout the day, pretend you're leaving, but then stop and just return to what you were doing. If having your coat on makes her anxious, wear it all the time, and take it on and off randomly throughout the day. Jingle your keys every so often, and put on your shoes and strut around in them for a spell. Open the front door and close it for no reason. Step outside the door just to step back in. When my puppy made the connection, backpack = mommy leaving, I used to wear my back when I got home, and took it off as I left, lol.
5) Leaving and returning, no big deal. I mention earlier that you want to be calm and nonchalant when you're leaving, also the way you leave can be important. If the dog can see you when you leave, sometimes leaving the door backwards makes them less anxious. Leaving backwards has less of an impact than just walking straight out. I'm not sure why is this so, but what I think it would be: face the dog = coming to the dog, back to the dog = leaving the dog. Facing forward I guess gives the dog the impression you're just standing on the other side of the door, lol. When you do get home, do not say "Hello" to Bear, be calm and act like it's no big deal. Think of it like, if she was anxious the whole time you were gone, if you throw her a party when you return, it just becomes a be reward for being anxious, and it just amplifies the fact that she was alone. Ignore her when you first get home, don't talk to her, don't touch her, don't even look at her, you want her to be calm before you say "hello". If you have to take her to the potty right afterwards, don't make a big deal. If she destroyed something, or had an accident, don't fuss, don't get angry, it already happened and there's nothing you can do, just be stone-cold. Also if you make a big scene about the returning home, sometimes the dog makes the connection that destruction brings you back because you're excited at the mess, lol.
Lastly, about her over excitement towards other people, you want to put structure to how she reacts to them. Have her on leash when people visit, and do not let her greet your guests on her own. Make sure your guests don't give her eye contact, touch her, or talk to her; tell them to ignore her. Get Bear to sit and wait calmly, when she is calm, give her permission to greet; give her a cue "Say Hello" or something like that. When you see that she's getting too excited, step back and wait for her to calm down again. This applies to anyone on the street, she is not allowed to greet unless calm. Even if you don't say "Hi", she not allowed to approach or sniff them without permission; not everyone wants to say "Hi" after all. When she gets excited when she sees someone, even if they're passing the window, do not react. Some people like to unintentionally rile up their dogs by going "Who's that?" or "Ooooo What do you see? What do you see?", this only rewards the excitement and make them even more excited. When she is like this, get her to calm down the same way, tell her to sit or distract her with something else. Don't ever reward the excitement if you want a calm dog.
Remember exercise and training will help you a lot. I hope this helps, lol. I'm so sorry for the long post.