Hi! I believe I can be of help with this issue.
First, let me say I can imagine how worrisome and confusing this situation must be for you. I am assuming from what you've written that there aren't any other major symptoms of any developmental problems or you would have reported them along with the incident. Our main focus here is going to be on the fact that you have only one incident to go on. That is enough to make you worried, but not enough to take action. That means observing, keeping watch without being obvious about it.
It is possible that she may have some developmental or behavioral disorder that is emerging. But that isn't necessarily likely. What we're looking for is information. You have too little of it. We don't know if we're facing a behavioral problem, a neurological problem, or some disorder problem (I don't want to name them at this juncture because you'll get scared and think the worst). We just don't know. What we need is an inventory of symptoms to be able to take to a child psychiatrist or psychologist for an evaluation if the behavior continues. Because her behavior so far is not conclusive.
Another little girl invaded her space. Her closet, her clothes, not only her mom. Remember: the girl invades her family and now she invaded her very clothes. That's a lot for a little girl. That she wanted to control the girl's actions sounds on target: minimize the fear of what else the girl might invade in your daughter's life. That she overreacted is not worrisome in itself. That is was so violent is what you're observing. But it's not more than that at this point. This is enough to explain the behavior in most kids and probably her as well, but you need to be watchful.
So at this time you need to give age appropriate incentive to adjust the behavior and be watchful if there are other symptoms coming up that you might need to begin to act on. And if our little chart and stickers fix the problem, be glad! But there's more for her.
Remember: it sounds as though she has to share mommy with other kids because of mommy's work as a babysitter. That's not easy for her. So you have to also reward as well as punish: WE are going to have so and so play with US today. If WE can be hospitable (play with the word and explain it well) then WE can have a treat. Notice the highlighted words here. She needs to feel she's still your special girl. That it's you two who are having this other girl or kids in the house. It's her house to is the idea.
Let me give you the name of the classic book for working on the anger and better ways. You can read them with her on your lap and make them age appropriate if they are older than for her. But first a book for you to help with skills:
Setting Limits With Your Strong Willed Child by Robert MacKenzie. It's available online.
See if she'll cuddle and let your read to her these books. Here are some great books to work with:
What to Do When Your Temper Flares by Heubner and Matthews.
How to Take the Grr out of Anger by Verdick and Lisovskis.
When I Feel Angry by Cornelia Spelman
Okay. So use these principles and don't try to rush this. As I said, you need to observe. But most likely you've got a feisty, sweet little girl who's trying to do more than she can cope with. I wish you the very best!
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