Your mom may be legitimately hungry as some people dont feel satified on the early stages of the diet. Things change however with firm/dense protein intake. Also some people still want to eat solely for the joy or comfort of it, so that may be a factor as well.
Reflux (which may mimic hunger pains) should be considered and meds usually given early post op to help. Is she taking anything?
Also a drastic change in lifestyle and other medications entering and leaving the system can affect sleep and mood as well. Start or stop anything recently?
Also a reasonable amount of time to completely heal and return to normal is important. Some people don't bounce back quickly. Patience is important but be aware of sudden declines as people should get better with time.
When you say she drinks a lot of water (but cannot urinate) i think in excess of the recommended 64 oz daily. Is this what you mean as well? Is there a way for you to track exact amounts (good info for doctors to have) ?
Perhaps it's time to split up her questions to different doctors besides her bariatric surgeon. They only handle the one thing.
Perhaps speak with the Primary to see if there is a need for a visit to the Urologist and also mood/mental health referrals for a Therapist.
If I was someone going through this I would ultimately just want to feel completely supported. Try to be patient and tolerant, let her journey be self guided but advocate for her when she needs you to.
Good luck💖