My female betta fish wont stop attacking my other females?

ok so i got a female betta fish and she is lager then the 2 new ones also older i was told they are fine in a small tank so i places them in with each other and she will not stop chasing them or darting at them what can i do to get them into the same tank without killing each other and i don't think a bigger tank will do it she seems to really hate the other 2 any one ? i cant get another tank so ya