I haven't had the surgery yet, but I will tell you that the reason is a combination of both. Right now at 275 pounds and size 22, I can't wait to be of normal weight and size again. I want to look great for myself and my husband. In the other hand, I also want to take the pain out of my knees, lower back and feet, be able to get down on the floor, play with my toddler and get up again without having to push myself up with difficulty.
I don't think that thinner people understand how an overweight person feels. When I was a size 9 I would have never thought about this, I even wonder how people let themselves be so big, and look at me now.
So, I don't think there is anything wrong to want to look great and feel even better. Support your mom and I wish her the best.