Down Home Daddy by Rayanna Jamison

Nobody is more shocked than me to find my childhood sweetheart on my front steps, asking me to make good on the pact we made over a dozen years ago.
Turns out, she’s found herself in rather desperate need of a husband. And she seems prepared to do whatever it takes to land one. Even accepting me as her Daddy, just the way it was before.
The first time I take her over my knee, our old flame doesn’t just spark again — it becomes an inferno, and it isn’t long before it consumes us both.
But old lovers come with old wounds, and Millie Sue has already broken my heart once. If we can’t find a way to heal and trust each other again, our marriage may be over before it even begins.