Feeding baby?

My friend has a baby that is one month younger than mine (she is 2 1/2 months). I feed my son whenever he is hungry. And at that age I thing he ate every 3 hours or so. She came over for dinner last night. Her baby is very small and they say it is because she has kidney problems. I noticed her baby just kept crying and she kept sticking the pacifier in her mouth and she would spit it out and cry the whole time pretty much. I told her I think she is hungry. she said she ate st 5 and wasn't allowed to eat again until 9. She then gave her baby water to tie her over. Then when she fed her at 9, the baby was full off of water and hardly ate. Then at the dinner table she gave her baby a little potato, just to let her taste it. I don't know maybe I am wrong here, but is she doing things wrong? I didn't want o tell her anything, but I think she needs to be fed every 2-3 hour at that age.