What size tank and with how many angels?
Generaly, it is not advised, but you could try (a minnimum of) 4 female bettas with 2 (adult) angels in at least a 30 gallon and see if it works out. Oftentimes, with these particular fish, it comes down to the individual's character.
Alternatively, if your mother realy likes bettas, maybe this is a chance for a new tank. You can keep a single one in a small (2-2.5 gallon or more is best IMO) bowl.