Candi likes making someone else tap out for a change.
What she may not have realised is that Mystique isn't a rookie. Quite the contrary, size aside she has beaten bigger and stronger.
In this case she has been over confident and careless, and Candi has gotten very lucky.
Mystique is throwing herself back trying to shake the hold.
It's not just the pain, it's the frustration that she let this happen.
Whether she has to tap here or not is perhaps academic. Candi now has Mystique's undivided attention, and the probability is that the near future will be filled with a lot of painful reprisal.