Human Cozy wants to drain magic from Equestria and give her self ALL the pure magic power. This will make her god in the human world and break the stone spell on her other self and will complete the attack her other self tried and failed to do to Equestria and no pony will be able to stop her from that other end.
Unware that Cozy Glow attacked nd banished the human Flurry Heart (sending her some place where its likely she died but maybe didn't) , the pony Flurry Heart trusts her unware that Cozy wants to repeat her crimes on this other Flurry