She likely isn't sitting when people come and you ask for a sit, right? Or if she is, she's sitting for a millisecond, then popping right back up. If this is the case, asking for a "sit" could actually do more harm than good.
Set up a training scenario. If you live with family members, you can start with family before progressing to friends, then strangers. Otherwise, start with a friend as your helper.
1. Have your helper go outside your door. (this is assuming you are the primary trainer/handler for this dog. If you are not, have the primary handler perform the steps for which I say "you") Preferably, have the puppy not know that they are on the porch, or at least wait until the puppy loses interest. Bring the dog to the door and have her sit. (far enough back that they will not be hit by the door when it opens)
2. The helper should knock or ring your bell. If the puppy gets excited, it's okay if she breaks her sit. Wait for her to calm down before asking for a sit again. If the dog gets extremely excited, repeat this step a few times until she can be slightly calmer. At this point, she is still allowed to break her sit, as long as she is not so excited that you can't get her to sit again.
3. Once the dog is sitting again, slowly open the door. The second she breaks her sit, close the door, even if you only got it open less than an inch. Wait for her to calm down again, and then try slowly opening the door again. Keep repeating this, the dog should eventually understand that if she breaks her sit, the door is closed. Keep practicing this, you should eventually be able to get the door all the way open.
---Depending on how long this took, you may want to take a break and do the rest later.---
4. Once you can get the door completely open without her standing up, have your helper start to come in. The puppy may get up the second the other person moves their foot slightly, or she may hold her sit until the person is already partway in. Either way, the second she breaks her sit, close the door in the helper's face. Keep doing this until the helper can come all the way in. Have the helper close the door behind them, but if the puppy breaks her sit, have them go back out.
5. Eventually, work up to where the helper can come in, close the door, walk up to the dog, and pet them, all without the dog freaking out. You may choose to allow the dog to break her sit once the person pets her, or you may still require a sit, this is totally personal preference. Either way, if the dog jumps up or does anything you don't want her to do, the helper goes back out. If she does what you want, the helper pets her, gives her treats, and/or plays with her.
At any point during this, you may need to go back a bit, which is fine. But dogs can generally, not always learn this in 1 day with family, and in under a week with friends or strangers.
Never allow a guest or yourself to pet her when she's being wild following your/their entrance. She shouldn't get ANY attention- this includes saying "no" or asking for a sit- until she's calm. If you ignore her, she'll eventually calm down. She only gets attention when she's calm, but once she is, make it a little "party"
As with any behavior problem, be sure that your dog gets enough mental AND physical exercise throughout the day.