if you choose talk from the radial menu of a PC and talk to the NPC, you should be able to select an option similar to "please leave the group." Some NPC's have a certain place they need to be in order to leave, and Fruella (maybe others, I'm not sure) won't leave short of death. If you're roleplaying, just have them get into an "accident", or keep them, otherwise you can just kill them.
