I hope you don't mind me answering. My ww is on hold until I have baby #2, but I've been back here lurking around!
Years ago, before I had my kids, I really worked hard and lost a lot of weight. I had always been an over weight kid, so my parents weren't supportive for two different reasons.
My mother did as yours did, was saying it was unhealthy and I should eat (bare in mind I was still technically over weight just smaller than I was before), but my own mother was always overweight (now obese) with an addiction to food and never was able to lose weight but would say from time to time how bad she felt. In fact, when we would go out for a lunch, if I ordered healthy, she would pick on me and actually get nasty because at the same time she'd order something unhealthy. I stopped going to lunch with her because she wanted a partner in crime to eat eat eat jumk with her, and when I stopped being that, she became very nasty. (my mother also have a lot of other issues at play in this)
It took me most of my 20s to see she was not worried about my healthy but angry that I had lost weight.
I'm not saying that I your mother's motive, but sometimes when we commit to be healthier, like eat healthy and exercise, the people (which can included family and friends) we previously "bonded" with over unhealthy habits (like grandma's home made apple pie, or sitting on the couch after dinner to watch tv with the family) feel let down that those times are changed.
I'm not sure if I'm making sense, and I'm going to blame it on mommy brain! lol, but also, some parents feel as though they are taking care or showing love through food, and not eating their super fattening home cooked meal can be received like not accepting a gift or even a hug.
You can try a few approaches. The nicer way would be to try to find other ways for you and your mom to share time rather than just over a meal. See if she will go for walks with you after dinner, so the part to look forward to is the walk after the meal rather than the meal itself. It would be a way of including her in your new lifestyle and would help her health at the same time. Trying to inform her and include her is the best way to go. Some people will respond to that and some want no part of it, and might continue to pass comments.
The other way that I used after all else failed and the comments continued, was to just agree with everything they say, but continue doing what your are doing. If your mom say you are to skinny, tell her she's right. Don't argue, or defend yourself against someone who has no intention of ever listening, meeting you half way or changing their outlook. It will only give you stress. Just put an end to the conversation and leave to room. If you've lost 60 lbs, then you have put a lot of time and effort into this weight loss and it should be obvious to your mother that her comments are falling on deaf ears and that you are not going to be swayed to gain wieght back by what she says, and since that has not curbed the remarks then maybe her comments are more to stir the pot than a futile attempt to get you to gain your weight back.
HTH