I agree with the poster who said discipline doesn't always work immediately like we want it to. Your only option in stopping this is to be firmer and more consistent for as long as it takes. She is still at a young enough age where explaining is useless and actual consequences are what it takes. Taking away stuff in and of itself is no big deal, especially if she's used to it. It's sort of the omission of a consequence since she still has lots of other stuff.
My daughter has been firmly disciplined since age one. (rarely needed because nothing was able to escalate). She's always been super super good. None of our kids have ever been allowed to interrupt, dominate adult conversations, or talk back in any way, and any small signs of bossy-ness were dealt with immediately and firmly ALWAYS toward us, each other (unless they're playing) and with other kids at parks etc.
Conversely, if people are being bossy to her, I tell her, "You say, 'you are not being nice, I do not want to play with you' and walk away" since about age 3. Because we are firm with our boundaries, and help her to be firm with her boundaries, she is very confident, and well aware that politeness will be enforced. She understands what bad behavior is by learning not to tolerate it from others as well, ad tells other kids when they're being rude.
BUT. 3/4 of the way through K4, she was pushing boundaries. I took it very seriously, reminded her I had eyes in her class and I would speak to her teacher EVERY day to make sure she was being respectful or there would be consequences. (spanking and favorite blanky taken away). She hasn't been spanked in 2 years, but just knowing she could be, and even worse-her favorite blanky which has been more of threat since she has outgrown spanking because it is her ONLY favorite thing, all her other stuff is just blah, but her blanky is her FAVORITE THING. I've only taken it twice briefly and she really was devastated and fears it happening again. This threat of both things happening (which would have been followed through on) nipped the problem instantly and was neither was needed, but that's a result of her long, firm foundation so there was no misconception about the behavior or the consequences. She has gotten nothing but flawless behavior marks ever since, but if I had needed to enforce, I certainly would have and would have compounded the consequences if necessary for as long as it took.
You have to be firmer, and you can't give up. Let her know specifically what is not allowed, and that you will ask the teacher every day and specifically what the ramifications will be (firmer than some removal of things if it's not deterring her) if she is not being nice to people. It will work. If you are firm enough, she will be a polite child through grade school, and she will have friends.
We lavish constant praise on all the kids. I cant' help it, it's sincere. I don't buy it that it damages anything unless you don't have discipline in place as well.
Depends what you mean by "You've let her know you're in charge" Does that mean you "told her you are in charge" or you have acted as such in no uncertain terms and it has SUNKEN IN. For all the youngest years, actions speak WAY LOUDER than words. If she feels like getting away with this behavior despite your reactions, chances are, you're not all the way in charge. Many of my friends remove toys alone from their kids, and they have chronic behavior problems. They just don't care. They're luxuries anyway, not necessities.
My step brother has 6 kids. 3 are "handfuls" but one (5 yo) is SUPER DIFFICULT!!!!! Where all the other ones will turn around with a warning or a swat, he needs: a swat, plus the removal of a favorite privilege for a while which he needs to earn back with a week of good behavior AND, after his spanking, he has to do a hard chore like haul the firewood or something. He's a super good kid, and only needs it rarely, but the rest weren't even acting up by this age. Some kids are tougher! Just keep in charge.