The thing that gets me most out of everything you have said is the idea that her coming INTO YOUR BEDROOM, WHILE YOUR HUSBAND WAS UNDRESSING was somehow innocent. Watch Single White Female (in fact, invite her around for it for movie night) and you will see what I mean.
I had a 'friend', a housemate actually, steal a boyfriend and one of the things she would do was insert herself inappropriately (physically and metaphorically!) when I had my boyfriend round. The whole turning up at 11pm when the two of you were in bed together struck a nerve as I once found my 'friend' curled up with my boyfriend 'watching a movie' when they knew I was due to be out at the theatre (both relationships ended after that) and I also once found her sat in the living room underneath my bedroom after I had been having sex with him.
I can imagine that the OP's 'friend' did what she did as both things, turning up to movie night, and turning up to your house when you were in bed with him were both overly intimate/boundary overstepping things to do, which could be plausibly brushed off. She was just engaging with friends right?
Her being all over your place all the time also means you can't have a private confrontation with your husband, resort to snipping and then YOU come across as the unreasonable one. It also means that if you do eventually confront him, it might be with her there, and both of them, plus perhaps her husband can all call you crazy. She is taking away any balance you might now have in your marriage.
This ex-friend of mine also had a habit of Wendying other women/mutual friends of ours. The 'oh dear I seem to have gone to lunch with your whole family without telling you,' thing was classic. So was the passivity of the others who should have had more loyalty to you. People are shit. I am sorry. It is a very nasty type of erasure that doesn't get talked about enough.
The fact you think your husband 'forgetting to tell you' that he had made plans with this woman, that sort of seem to include you though not consider what you actually want, is something you should 'feel stupid about' says a awful lot about the role you are playing in this and why a woman like this has made you her mark.
You have been told the same thing over and over about how to handle this by other posters, I'm not going to add to that chorus. While my situation was different to yours, he was not a serious boyfriend at all and yours is a husband, I think it is worth pointing out my ex and ex-friend are now married. All our mutual friends went to the wedding.