Why didn't The First Evil ever take the form of Willow?
She technically died in season 2, episode Halloween. She died and became her costume as a ghost, so the first could have appeared as Willow too.
Especially in the first episode of season 7 when it took the form of all the previous Big Bads, Warren, Glory, Adam, the Mayor, Drucila, and the Master. It should of appeared as Willow as well, in my opinion.