Hi and welcome back!
I have heard of people with BPD having flare ups as you describe though I never experienced that myself. Flare ups with so long in between sounds like it would be very hard to reconcile the extreme changes. I do know that steroids can really set off anger in a lot of people. For me, when I have had to take them, awareness was key to anger management. I don't suppose your mom is too good at that though?
I am so conditioned to just want to make her happy, but I know rationally there's nothing I can do to make her happy, and the more I try the more she gets upset. For Christmas I got her a new iphone (on my plan, hers was really old). She was openly upset with me over it because she didn't want a new phone and had an attachment to the old one.
Knowing something rationally is totally different than knowing on an emotional level. I think we have all experienced that. I am sorry she is reacting this way. I am sure you know that is all about her and has nothing to do with you but... .that is all about her and has nothing to do with you.
I don't know. I feel so conflicted and sad over all of this. She was so mean to my husband which is unacceptable. When I tried to confront her about it she said she wasn't mean, that I'm the mean one, and that she's only mean because I'm mean.
This sounds like Projection and FOG to me. Are you familiar with those? We have articles I can link you to if you want them.
I agree that this is tiring and it sounds very stressful, especially when she is insulting your husband, living in your home and still complaining about it and finding everything you do to be wrong. Have you ever tried setting boundaries and limits and saying no to her before? What do your boundaries look and sound like when you set them? We can help if you want to try changing things at your end of the relationship. I am not saying you are at fault at all. Nor am I saying that changing you will fix her... .it probably won't but you can make things significantly better for yourself.