Potentail slayers (capable of be the next slayer)are just normal humans. Just like Buffy was before Giles, her Watcher chosen her to be the next slayer, after Spike killed Kendra's mother, a slayer. Spike took her leather trench coat as a souvenir for the kill.
The Master drain Buffy of her blood and throws her into a pool, killing her. Wes, a Watcher, immediately summon Faith, a potentail, as the new slayer unaware that the old slayer, Buffy wasn't really dead.
Only Watchers, demons, or vampires could tell if someone is a potentail slayer.
That's why Angel knew Buffy was the slayer before Giles appointed her, with the help from his demon pal who find her.
Watchers can only appoint potentail slayers to be the next slayer. It not like they can pick just anyone.
Now, there can't be anymore new slayer since the Watcher council was destory. Buffy and Faith are the last slayers. Faith really should've been the the only slayer, since Buffy was killed for a second time when she took her life for Dawn at the end of season six. The series should've edded with that.
I didn't know Spike killed her mother. Where's this said?
1900: Spike kills his first Slayer during the Boxer Rebellion.
Kendra's mother was the first slayer Spike killed. He took her coat as souvenir for his 1st kill.