People who could have killed the great mother
Rhinos: we know the rhinos hold a grudge against the Elephant and that rockslide and his crash are particually agressieve
Titanpride: he may have seen her as a threat and killed her
Stinger: although he obviously did not do this himself he may have convinced someone to do it for him
Cheetahs: although less likely they may have done it due to anger toward her and standing within fearless