On her front

One of her favorite ways to get herself off was to lie on her stomach and reach down and rub herself.

I once walked in on her like this. I'd stayed over at her place, and then left in the morning. I was in a hurry and we didn't have time for hanky panky. I rushed out, but forgot something. When I came back, I found her on her bed, rolling around on top of her hand, her butt clenching, like she was humping her hand.

She was just on the verge of climax when I caught her. She was shocked, half zonked out in sexual la-la land, and really embarrassed. 

I told her I'd stick around to watch if I could, but that I really had to go.  I kissed her as I dashed back out and told her it was totally sexy and that I'd be driving to my appointment, thinking about her up in her room, finishing what she'd started. 

She smiled as I hit the door. 

As I drove to my appointment, I knew right then she was home, finishing up, having a good powerful climax on her bed. I knew I'd keep the image in my head all day, and when I got home, we'd have passionate, inspired sex.