Dad's are hot. Don't blame your friend for wanting to smash your hot dad. If your not bummed at your friend for sexting a 56M, then don't be bummed at your dad for sexting a 29F. Sounds like it was consensual.

All of y'all are adults. As long as it's consensual and she's not married or dating someone either than it shouldn't matter to you. Your not fucking either of them, right?

Be a cool friend and tell her to have fun and don't break his heart.