Quoting Narcissus ™:" *sigh* and here I thought I was being a bitch.. I know her mom is diabetic, and yes her parents ... [snip!] ... urine is pungent, KWIM? ETA: she has a sedentary lifestyle. So do we, but we try doing as much as we can as often as we can."
I don't think you are being a bitch at all but I think you are going to have a lot of attitude coming your way and you shouldn't think she's just being bratty. It's what she's used to, it's going to be confusing and upsetting to go from getting to eat whenever she wants to a regulated schedule. She's not going to understand so try to be patient with her. Not that I think you are or would get upset with her but I just wanted to throw that out there.
I'd work on her activity level too. When we are stuck inside and my kids are burning with energy we sing songs like ring around the rosy and dance in a circle, sometimes I make them "cheerleaders" and make up cheers for them to learn. I'll give them dress up stuff and tell them to do a dance show for me. It gets the wiggles out and it's a lot of fun for them. I think it's really great that you care about her health and want to help!!