He meets Rebecca and Amanda in Legacy. For some reason I was thinking that the flashback of her taking her first head was in MG. That may be wrong, but didnt' Duncan ask her why she was going after Methos "why are you doing this?" and she said it was because she was tired of being afraid. Then they went to the flashback. And we didn't see her take a head, only that she was running and Rebecca made her stand up to him.

Let me know if that second one is wrong though.