So many questions. I'm hoping your aunt is a nurse or dietician? so sorry OP. If your swim coach is anything like mine was he will probably be giving you a lot of crap nicknames and jokes.
I assume the aunt is a nurse or doctor of sorts and the mom may have been having intestine problems, or digestion system problems as a whole. Or the two just have an ongoing joke. Or she was trying to tell the aunt that she's a piece of shit by just sending a picture. Who knows though