One of the assistants at my local Asda had this type of surgery about a year ago. She has lost a lot of weight, but says she regrets her decision as she is in constant pain, which cannot be resolved. I don't know if this is a common problem or a rare unlucky outcome.
I have battled with my weight for years, always regaining. However, I have acheived lasting success (so far) with alternate day fasting. Perhaps you could point the member in the direction of the various threads on this subject, including 5:2, in the diet section. She will find lots of support on GN, not just local, if she feels able to raise the subject. Please pass on my best wishes for a successful outcome. 