Getting older...

So, I have a few rabbits in the building now that are getting on in age.  Haze, who is my baby, is now 9 years old.  I give her unlimited feed, occasional hay, and now that it's spring, she gets plenty of dandelions, grass, clover, branches, etc.  She's doing great.  She has plenty of energy, she still likes to dig, and roll, and run.  Sometimes she gets a bit overweight and I cut her back on her pellets and feed her unlimited hay.

Cotton, on the other hand, (who is Haze's 8 year old daughter) belongs to my mother.  She has recently started to lose weight very rapidly.  I'v felt a mass in her pelvic area that does not move and one in her abdomen that does.  She hardly eats her pellets, but I keep her dish filled.  She's not really interested in hay, but I make sure she has it.  I give her black oil sunflower seeds and gobbles them up.  Everyday I give her a giant handful of dandelions and she sits and eats them until they are gone.  She eats grass when you give it to her, but I don't know if it will give her gas by eating too much.  I'm not sure what to do.  I just keep feeding her because I feel that is better than her not eating at all.   She's at the age that I feel like it's not worth putting her through any invasive procedures in this point in her like. I just want her to be comfortable until my mother makes the call to get her put down.  Any suggestions are welcome.