Boyfriend21

My finance is a 21 year old beautiful young woman. She is approximately 5'9" tall, weighs approximately 290lbs. She has been diagnosed with PCOS, which in my opinion, is a large cause for her current weight. She has medication for the PCOS but has a difficult time remembering to take it regularly so I do no think that it has much of an effect. Other than the PCOS, she has no health issues. Heart is good, BP is good, blood looks good, everything.
She wants to get lap band surgery. She talks about the long term health benefits of being thinner, but when it comes right down to it, she wants the band so she can be thinner. She has been a bigger girl all of her life and she wants to be that thin stylish girl. No matter how much I tell her how beautiful she is, etc. she always feels like the fat ugly girl, and she wants to be thin.
I have read tons of information all over the internet and honestly I am terrified of her getting this and it making her miserable for the rest of her life. It seems to restrict so much of what you can eat and drink. I read that some doctors tell you to stay away from certain activities to prevent you from flipping, etc. I read about ulcers and vomiting and all kinds of things.
I want to be supportive of her decision in the worst way, but I also do not want her to do this and spend the rest of her life regretting it.
Am I being overly protective? Is being thin really worth the possible risks when you currently have no health issues? Are the issues really less than it seems that they are? Help me out here people. Either tell me I am off the mark and I should encourage her to do this and make herself into the image that she wants. Or should I encourage her to pursue other less evasive methods of weight loss first? Please help! I love her so much. I want her happy, but I want to keep her healthy too and thin doesnt always = healthy.
Give me some insight please.