My dog has a weird kind of dog aggression/resource guarding I need help with

My dog Hazel is a 4 1/2 mini schnauzer mix, she is the sweetest thing but she’s protective of course, she very much thinks this house is “hers, not any other dogs but they can live here if they need to” so she’s not aggressive to my older sisters dogs 99% of the time, but when it comes to her little toys (about the size of a large rat) she gets really fussy over but it’s only sometimes. Most of the time my older sisters dogs and grab hazels toys and play with them, but if she has them and they try and take them she doesn’t growl much, sometimes she will (resource guarding it) and sometimes she yells at them (I’ll explain in a moment) and other times if my older sisters dogs just look at Hazel weird she escalates a lot and does the same. She’s also a big advocate for her space and will correct them, only she doesn’t stop pretty much

I’ll explain what exactly she’s doing, she makes almost a snarling-bark sound and stands on her back legs with her front on whichever dog she’s yelling at, pushing them. She doesn’t bite or snap at them she just pushes them around and yells at them. She hasn’t hurt anybody but I don’t want it to get to that point.

She also does this when she’s playing with one of them and she decides she’s done but the other isn’t. For example, my older sisters dog Parker whom is a big pitbull mix (he does have apbt) puppy loves playing with Hazel, they’ll run around my legs and under beds and play tug of war, but he’s a big puppy who never wants to stop so of course she yells at him (gets him to stop) but I’ve gotta break it up cause he’s big and clumsy, she’s small but forward, somebody would get hurt

I hope this explains properly ;-; I went through the wiki for both dog aggression and resource guarding but Hazel seems to be very specific with it cause she’s fine over half the time and then randomly she just snaps at them, big dog, little dog, doesn’t matter to her. In her head she is the big dog of this house