My EF wants me to go with her and hold her hand while she gets her hoo-hoo pierced. Is this wrong?

If she wants a piercing in her "hoo-hoo" she is grown up enough to go by herself. This is something she is electing to have, not something she has to have. Since she is all grown up at 20 and a half and knows what she is doing, then she will know how to handle this without you holding her hand. She should ask her mom to go with her.