I am currently maintaining a 65 pound weight loss and am only a few years younger than your mom. I also have bad knees. Many years ago I did go to a weight loss spa for a week.
The question you ask is a complex one and there is no one answer that works for everyone. I follow a number of weight loss blogs (and have one of my own) and I've learned that different people need different things. Just some thoughts:
1. What does your mom want to do? Does she want to go and stay somewhere? Does she want to lose weight? What has worked or not worked for her in the past? I know that for me some things worked well for me and some didn't.
2. On going and staying somewhere, it is unclear to me if you are asking about some place for a long term stay to lose weight or if you are talking about a short visit to a weight loss spa.
When I went to the spa (many years ago), you could choose to go to classes for fitness or not go to them. I wanted my money's worth so mostly went. However, I was not fit before I got there and I couldn't keep up with most of the exercise. I was soon sore and miserable. If your mom isn't used to exercise an intense exercise spa may not be a good fit for her. Also, I know that with my knee I can't exercise for several hours a day. My knee won't hold up to it. I know some people feel these places can be a good jumpstart for someone. It didn't work that way for me. On the other hand, I could see going to one to try to get the last couple of pounds off once I was already in good shape. I'm not sure of current costs, but I researched it a few years ago and there was a wide variety of costs.
There are also places that people and go and stay for a long time to lose weight. I have heard of the
Duke program, but have no experience with it. It is very expensive.
2. For most people, no matter how hard it is to lose the weight, the most difficult part is maintaining weight loss. Most people regain a significant amount of weight lost. Part of that may be due to burning fewer calories than expected after weight loss and some may be due to increased appetite after weight loss. Regardless, I have found that what has worked the best for me is to find a way to eat and exercise that works for me in the real world and that I can sustain in the real world. I personally found that Weight Watchers worked best for me. But, this is all very individual. That said, I found the Weight Watchers weekly meetings really helped me to structure my week and to stay accountable and keep my head thinking about weight loss.
3. Depending on your mother's weight and whether she has any health conditions she might qualify for weight loss surgery. I'm not advocating it or not advocating it, but it is an option for some people. Another option for those with serious obesity who don't want weight loss surgery may be a medically supervised weight loss program. Some hospitals have such programs. In some instances the hospital may have exercise programs available as well.
4. I do think a trainer can be helpful for the physical activity part of it. Most trainers I've had though haven't been very knowledgeable about weight loss.