Depends on whether she raises her head.

As pictured:

• Depending on the ammunition, her ass jiggles either sightly or substantially
• Her hat is probably displaced
• She wishes she had doubled up on hearing protection

Lots of things could go wrong here but him pulling the trigger from this position is relatively tame. Stupid as fuck, but tame.

She will feel no effect from the barrel heating up as the other commenter said, for two reasons.

First, one shot doesn't really do much to the barrel temperature - you'd need multiple shots in relatively rapid succession (i.e. several within a few minutes) for the barrel to start getting uncomfortably warm.

Second, the barrel isn't resting on her gluteal cleft; the receiver is. This part of the rifle is designed to be held.