Hit the brakes.

"Riley...." you try to keep your voice level, but the wrongness of her behavior has set you on edge. Not to mention...the tent it's giving you that you wish you it wasn't. "Stop. That's inappropriate."
"Ugh..." she pushes away in a huff. "Inappropriate. Inappropriate. That's all I ever hear. 'Miss Sinclair, it's inappropriate to wear that to class.' 'Riley, it's inappropriate to fantasize about your father.'" She puts on a pout. "Well I like dressing sexy and I fantasize about who I want!"
"Riley, keep your voice down."
"Or what?" she crosses her arms. "Are you going to spank me, daddy?!"
That's it. You've had enough. You climb into the pool, heedless of getting your clothes wet. Before she can react, you seize her by the hair, and drag her towards the shallow end until you reach the edge.
"Ow..!! Daddy!"
"Be quiet, Riley. You're in a lot of trouble, and if you don't want it to get worse, you'll do what I say!" Your frustrations about the situation with Jenna are reaching a boil, and now this...
You drag your daughter across your lap. You haven't done what you're about to do in maybe 11 years. You strike her bikini clad ass repeatedly with the palm of your hand. At first, she doesn't give a reaction, but after the third strike, she starts to wail, and kick and thrash in the water until you pull her hair tight in your fist.
"Stop that. You're just making it worse." Soon, despite being nearly 21, Riley is blubbering like a 12 year old. Her ass is angry and red, and your hand is pulsing with pain as well.
Riley sobs as you let her go, putting her head on her arms as her tanned hide slides back into the water. "I'm sorry I had to do that, honey." You climb out of the pool, grabbing a towel to pat down your clothes. "But you need to stop that behavior. You're nearly a grown woman, and it's my last chance to make sure you're a decent one."
"Why.?..I.... just wanted to make you feel goo...oood...." she blubbers.
"That's not your job, Riley." You sit down next to her. "It's not your concern. Your only concern is being a good girl."
"I...I can be a good girl...for you daddy..." she looks at you with red eyes. She snakes a hand towards your leg.
"Jesus...Riley! Do you want another?"
"You can do whatever you want to me daddy, just please...." her hand reaches the hard cock in your pants. "...don't push me away."