[Someone]

Alright, so the last month, my just turned one year old pup has started to be reactive in certain situations and it really baffles me, I am not sure how to deal with it, and couldn't find much online for my situation.
So normally she will not bark "aggressively" at anything, not on walks, not at home if we got visitors or if we are somewhere where there is other people too.

I can give a situation I was in yesterday, we were inside a room with several other people, she didn't react to people outside, people walking in and out, she had settled down on the floor.
Speed forward a little bit, we were sitting there alone. She was still settled down, but now that she's alone with me, she will start barking when someone comes in the door, she will bark and growl at anything she see's moving outside.
If someone does come in, and she barks like that, she will bark until she's gotten close to them, then the switch will flip and she goes into super hyper happy greeter.

I can attest to that it's not frustrated greeter behavior, it's a lot more force behind these barks, she's also a frustrated greeter and the sounds from that are completely different.
I have been completely calm in these situations, so it's not my nervousness she's reacting too, she's not been on a lead. And it's ONLY if we are alone together inside a room she will act like this.

At home it's easier to snap her out of it, just gotta get her favorite toy/treats and play/train a little with her. But it did not work in the situation I was in yesterday.

Any suggestions on ways to train her not to? cause I can't let her lose and let her greet everyone that comes into every room, seeing some people are scared of dogs. And for those it doesn't help that she just keeps barking non stop.

 

[Shell]

Might be more towards a protective/guarding type bark or behavior? Since it appears when others approach or sound like they are approaching you and her.

Note that I am not saying that protective/guarding behavior is necessarily appropriate in that situation but that the base reason of the barking might be different

 

[CptJack]

Dogs are weird.

But I find pretty consistently that a dog is more likely to alert bark, guard-bark, OR become reactive when it's relatively quiet and there's a single stimulus than they are in a big busy environment.

I had my young (very, very stable) dog out among easily 2000 people today and it was fine.

But that ONE DUDE dancing on a street when we drove by was weird and made him bark.

And my actual reactive dog is better at an agility trial packed with dogs and people than she is in a park with one other dog 100 feet away because she NOTICES that dog a lot more.

 

[MastiffGuy]

What breed is she, because it sound like a Guardian breed?
Mouse will let all the people in the world play and walk by all day, but let one person walk by at night he is up and at the door, God forbid they touch the gate when it is Trish home alone with him.

Most guardian breeds know when there should be and when there should not be, so your dog knows when there a bunch of people it is normal but also knows when it is a solo person when others are not present to be careful of that person.

 

[Someone]

Mastiff, she's a GSDxStaffy(50/50) mix. So there is some guardian in her for sure.
Not sure though if she knows why she's barking seeing she'll just flip the switch even for complete strangers when she gets close.

Her bark is for sure a more guarding bark than an alerting bark, she's never been super reactive apart from the frustrated greeter part, but that is going away as we've lately been training her a lot not being allowed to greet every dog she meets, that was just my bad cause I socialized her too much, everytime we went on walks etc it was always off leash, and we went on too many playdates.

Cpt you might be right that she's just weird though, I can't really explain why she'd guard bark, seeing she loves literally everyone. And she's a very confident dog when it comes to most things, even when she starts this barking she'll run up to the person, and then ofcourse the switch flips and she'll wag her tail with her whole body and try to lick the person to death.
Do you have any suggestions to how to deal with it when it does happen?
And for how your young dog acts, mine is the same, does sometimes pick out a random person to bark at for no reason. But it's very very rare, think it's happened 4-5 times total.

If it helps any, she is SUPER high energy/high stress, All competing agility trainers I've met wishes they had a dog like her, if that makes you understand how crazy this dog is.
Done so much calming exercises with her since I got her, actually cause you guided me in the right direction, she's still crazy, but we are now doing agility to have an outlet for her crazy. And so far it seems to work.
Thinking this can be important information.