Honestly, I don’t believe in overused FCs in roleplays. The whole point of having an FC is to have a reference for what the character looks like, so players can visualize it in their head as they roleplay. If an FC is used often, it doesn’t really matter- it just means that they are well known and physically appealing to most people, and the admin figured they’d get more auditions for a character that had that FC. As long as the bio is original and not overused, then I don’t think it should matter what the FC is.
As for Rachel, I adore her. So I would highly encourage you to use her as an FC in your roleplay, overused or not (I do believe in underused FCs, just not overused ones).
Underused FC: Jessica Parker Kennedy
Underused FC: Holland Roden