Of course you're not wrong! If your aunt wasn't abusive when she was well, I presume that the changes in her brain are behind her current behaviour. But, that doesn't mean that you should have to put up with it, and if other family members think you are terrible for wanting to help get get into a care facility, then maybe they could take her in and look after her.

I suggest that you go ahead and organise a placement for her, and then get whatever help is available to move her out, even if it is the police. In the meantime, speak to the police about the situation and the threats of elder abuse charges your aunt is hanging over your head, and try to have the situation put on record, so that if she does follow through on her threats, they won't immediately accept them at face value.
Its an awful situation to be in; I'm sorry you're having to go through this!