From the size of Travis, it looks like she fed him well.
Her daughter was killed in a car accident and her husband died, not sure how, but from what I have been reading, her chimp became her world and a substitution for the family she lost.
Not excusing her decision to keep a chimp, or the poor and IMO dangerous, decision of the city to grandfather that animal into the animal ban, but I think she’s clearly not dealing with a full deck emotionally.
I’m sure she took very good care of him...