When Buffy died in S1E12 - Prophecy Girl (she was killed by the master), she was replaced by another Slayer and the strength was transmitted to another. So, when the monks created Dawn to contain the key and sent it to the Slayer, why was it sent to Buffy and not Faith?
An out-of-universe explanation is obvious: there would've been no story if Dawn had been sent to Faith. So, I am looking for an in-universe explanation why Dawn was sent to the old Slayer and not the current one.