Fiance's friend hates me

My fiancé (let's call him Robert) is friends with an elderly lady (Mary). He knew her husband too before he passed away. I was abused by my parents and Robert found out around the time we started dating by accidentally witnessing a horrendous scene where my father was beating me and yelling that he'd kill me.

Panicked, he called Mary for advice and she told him to ignore it, not get involved, cut ties with me because I'd just be "messy", etc. I found this out much later and was frankly stunned. My opinion of her went down the drain. Robert continued dating me regardless and helped me get out of my abusive home. (We're both in our mid-20s now)

Whenever we meet Mary she makes it VERY clear how much she doesn't like me. She drops all kinds of hints about how Robert could have dated other "cute girls" that they know, intentionally ignores me the whole time, leaves me out of conversations, and basically has an air of completely despising my existence.

I put up with it for my fiance's sake but she is unhealthy to him too - she often is passive aggressive and wants all his attention, which he obviously can't do anymore because he's got his own life. Robert's parents are from another country and feel indebted to her so whenever they visit, they ask to see her multiple times. I feel like if I don't come along, it'd be giving her satisfaction and I shouldn't let her think she can treat me badly till I just leave. On the other hand, Robert never defends me and just says I should "put up with it" because he'a indebted to her and she's an old lady, lonely, etc.

I call that BS. How would you handle this situation? It's easy to say grin and bear it but I'm losing my mind. She reminds me of my abusive and manipulative mother in the way she behaves (and she wonders why her children don't want to visit her or take care of her).