The comment to your husband would be my deal breaker too.
Why would a friend say that to anyone, let alone the person you are married to?
There was real nastiness there.
Whatever her reasons for saying it, her true colours were showing right there. Because it was either done to cause trouble or she genuinely believed that he would agree with her because she really thought you looked bad in the dress.
Good for him for calling her out on it rather than saying nothing to keep the peace or whatever.
She's sounding more and more like a nasty piece of work. She hasn't properly apologised, she's made an excuse, then called you overly sensitive and ridiculous (so blamed you for your feelings rather than herself for her actions) and still expects a favour from you.
Regardless of her unhappiness with herself, she's being awful to you and you don't deserve it.
From my own experience (not of weight loss, which I could do with, but of overcoming some self confidence issues) I have noticed that people don't like it when someone changes, particularly if it's a change for the better about themselves. Often people resent it, or feel criticised themselves by it, or worry about how your changes will affect them.
You clearly want to lose weight and are working hard at it, so for you it's a change for the better.
I took part in a course on self-awareness, which has made me realise that I didn't have to be a doormat all the time. I had grown up believing I lacked confidence and wasn't good enough, and had to put up with anything rather than rock the boat, when all along it's been something other people have told me I was, not something I really was. I grew up believing it, so it became true. Once I'd realised this, I felt more confident, I stood up for myself more, and I started a college course I hadn't felt I would be good enough to do and would never pass.
I've just finished my first year and came away from the exam with the highest grade.
But some people haven't liked it. They say I've changed like it's a bad thing, but I feel better, happier, more confident and I'm working towards a career I know I will love and which will improve my life and my family's circumstances. What's bad about that? Nothing for me, but the people who resent it have their own issues to deal with. Nobody should expect you to be unhappy with yourself just so they can feel better about themselves instead.
I would send cuntycowface's message or do as manatee has suggested and ask her to come in and talk, but only if you really want to try to save the friendship and move on. And you can only do that if she is prepared to take ownership of her behaviour. But I wouldn't blame you one bit if you wanted to just let the friendship go now.