We've HSed from the start (oldest is 11), so I'm pro-HS, but if things are going great in the current school and peer group, I'd be reluctant to change things up.

Unless you're planning actively avoid academics during the HS year, I wouldn't expect it to go well with undoing the skip. HSing may reduce her tolerance for boredom, and it doesn't take many hours per week for a gifted kid to keep up with a normal school pace.