Go to Evie/Selena and call Cephrina. Wait 2 or 3 days and Evie/Selena will appear on the map in the hideout with Cephrina on her head. There, Evie/Selena is being fucked by Cephrina and is naked from then on. You can then hire Evie/Selena as a team member in the hideout with Cephrina as a fashionable hat. Evie/Selena then fight naked except for their ugly hat. If you send them home you'll find them back in the hiding place where Cephrina is... what hats are up to.
If Evie/Selena dies during the fight you will find Evie/Selena standing naked in the hiding place without a hat.
BUT: From the moment Evie/Selena shows up in hideout with an ugly hat, Cephrina has taken over her mind and will no longer give it away.
I haven't found a way to make them Evie or Selena again. This means if you want/need to have one of the two on the team, you can only do it with Cephrina.
If Cephrina's influence is so low, Evie/Selena is the body owner again and Cephrina's "piece of cake" is barely visible (let's say 99% Evie/Selena and 1% Cephrina) Evie/Selena remains obsessed. Celica can eat a dwarf cake to cancel this effect, the two naked ones can't do that.
Even if they die heroically in battle, they only appear in hideout where they are naked but useless because you can no longer interact with them. Both are then completely out of the race.
Is it worth it?
With a save beforehand, definitely.