Tell her essentially what you just told us. Hell, show her the post if you want.

"I love you for a million reasons and not just sex. You don't have to do anything with me you don't feel like, and that includes sex or sexts. I love when we're together and I love getting dirty pictures but I just want you to understand that those things aren't requirements for me and if there's ever a day you're not feeling it don't feel forced, I promise it's cool."