My mom is the exact same way. It's totally depressing because I would say that she is truly my best friend and this is something so important to me. She's seen me lose 90 lbs and gain it all back in half the time it took me to lose it and still she says I should do it the "natural way".
I have news for you, Mom, it doesn't work!!
I have sent all the research I can her way but she still says all kinds of negative things about it whenever it's brought up which has caused me just not to talk about it around her and that kills me because I am thinking about it 95% of my time these days. Ugh. I wish I could give you a solution or find one myself. She says things like, "you know you still have to change your lifestyle", etc, but it a seriously negative, faithless way. I hate it.
I really hope that our mom's come around soon, or hopefully when the results start showing. She is obese too (but probably only a 30 or 31 BMI) and unlike me, she has comorbidities like hypertension. I don't want type II diabetes or hypertension. I want to put an end to the cycle. If I drill that into her enough, I hope she comes around.