What Causes Numbness In Labia Majora Area?

Hi Dr. Rynne: I was making love with my wife last evening, and started massaging her labia majora. She said she couldnt feel it and asked me to pinch it. I did, and I pinched it pretty hard, she couldn t feel anything but pressure. It seems to cover the entire labia majora, and into the space between the majora and minora. I ended up pinching all the way down to past the perineum. She s had a botched hysterectomy and then again a few months later to remove her last ovary. Any ideas? Dave