Gaslighting is abuse on its own or may be used to conceal other abuse. It is a tool used to control and to undermine. My ex lied to me CONSTANTLY even while I was literally holding the proof in my hands, “this statement shows you spent $400 on the credit card last month.” “I did not. You’re a f-ing liar.”
literally every single time he said he would pay a bill, he insisted that he totally paid it even though the dentist/city/mechanic says it has not been paid and they “didn’t give him a receipt.” He once went 2 months telling me that he “hadn’t gotten paid yet” at his new job, and then that they paid him for this week but not any of the non-existent back pay. this is just the tip of the iceberg. Eventually I didn’t know what was true about ANYTHING. And that was the point - that I doubt my own perception so that HE could shape the “facts” to suit his needs.

That said, it’s not clear from your description whether you are actually describing gaslighting or just two vastly different sets of perceptions. Is it possible that HER memory was bad? Was she intentionally misrepresenting? Did she use your “failing memory” to blame you for things, avoid responsibility for her actions or accuse you of things you didn’t do? Was it a reason why you “needed” her or did she enjoy messing with your head? That is, if it served some purpose or she had something to gain from it, it was probably gaslighting.

Gaslighting is 100% abuse. My college boyfriend did it all the time. "You can't be mad about that. I just care about you. You have no reason to be mad." Nah, man, you're a dick, and you did a dicky thing, and I'm totally right to be mad about it. It got so bad that I went to a counselor about it. Should've just dumped his ass, but he'd systematically removed my support system, you know, like abusers do. Sad thing is I saw what he was doing and let it happen anyway. Ah well, live and learn.

Was she changing the facts to make you doubt your own memory? Or was your memory getting worse due to stress?

Your initial question requires no debate. All are aware, or should be, that to manipulate another human being through psychological means that calls into question their own sanity, is inherently wrong.

I see it as abusive. Anyone who makes you question yourself is not worth being with and certainly doesn't care about your welfare. I've realized recently that my mother 'gaslighted' me about health issues when I was a child to the point that I almost died several years ago because I wasn't sure I was sick enough to consult a physician. I had pancreatitis and would probably have died had I not gone to the hospital when I did. There is a significant professional literature in psychology about the damage that gaslighting can do -- particularly in intimate relations (including parenthood).

Yes my ex did the same thing to me started pretty much the same small things at first then just blatent lies . Be glad you are away from her and can get your head sorted i still have to deal with mine because of my son . Now i write everything down save emails and texts so i can just go heres the proof .

Yes I would, sorry you had to go through that. I have people that are consistently like this in my life, I try and distance them and am aware of what they are doing...but it still sucks.