THIS. She does these things in order to manipulate you into doing whatever serves her purposes. And will frame it to make it look like anything and everything but. I was writing a post last night about it, then decided maybe it wasn't my business to say, but the more you write about it, the more I believe this to be the situation.
I don't have specific answers, but firm boundaries will be your best friend. Hopefully someone will be able to suggest some good reading, as I can't remember what book it was that first clued me in on the subject, but wow, was it ever a revelation! They are really really good to have. The one thing is that yes, if someone is used to using you as a doormat, they will likely not quite believe it at first and will test it (like kids, really). But it's one of those things. It feels hard to do early on, but makes things a LOT easier in the long run.

Just to be clear, I'm not saying you are a doormat(!) But I feel you on the fear of conflict thing. And how. And one so easily leads to the other. And it boils down to boundaries. (And I can relate to Flummixed too -- sometimes I can be explosive, so I really have to work hard to avoid -- or better, defer conflict to when I'm not feeling like a rabid wolverine -- like in a super irritable hypo -- when I'm not afraid of anything.)

Now, confession. Yes, I am still basically a doormat (decades of habit don't change overnight). But LESS of one. And can assure you that you will be unbelievably proud of yourself when you utilize them! Like, holy ****, that actually worked! And to not feel resentful and like crap about myself?(!) WOW! Double bonus points!