My version of last part.

Sandra tries to seduce Kenny after dinner and Lynda knew about her plan but because of the guilt of their daughter she remain silent. But in bedroom even after so much efforts she came to know about Kenny's disability. This makes her so angry that even after so much efforts she didn't get what she want. After some days Sandra came home late at night with some stranger and while Kenny asked about him she told him to back off as he is not able to give her anything. And these things continued. She sometimes took her colleagues with her too. Lynda was also surprised by Sandra's actions. After sometimes she made their home a place for her enjoyment and when they object she mocked them in front of everyone. But as she was his legal wife now they couldn't do anything. But one day she pushed Lynda from stairs which actually turned into blessing in their life and her condition recovered. Kenny gave divorce to Sandra and they had a baby again.