since your mom has undergone surgery for burst appendix
, her bowel movements at this point may be irregular. and its quite natural. hence your doctor has put feeding tube( Ryle's tube- both fr feeding and for draing stomach content if bowel is not working). since shei s not taking adequate food oraly her stool will be green because it contains lots of BILE . once she restores her bowel movements she will be fine. i hope this answer helps you.
take care of your mom