My family and I are staying at my eldest sister-in-law's house while our house is being renovated. Thirsty in the middle of the night...

My family and I are staying at my eldest sister-in-law's house while our house is being renovated. Thirsty in the middle of the night, I went to the kitchen to get some water and was surprised to see this. My eldest sister-in-law must have known I saw her, but instead of ducking, she's riding me even harder and more voluptuously. She's got a fully automatic dildo on the seat, and she's pumping it as she rides it. Looking at her slutty posture, she must be enjoying it. What do you think? Should I immediately use my big cock to fuck her and give her even more pleasure?