For a few years, I've wondered if there was a possibility that Judge Elizabeth Donnelly could've been the mother of Kathy Stabler? During Christopher's tenure on the show, Elizabeth and Kathy did not share any scenes together nor mentioned one another. However, during seasons 6-8 Kathy and Elliot were separated and she was living with her mother; Kathy did refer 'my parents' in season 1 so that would mean that her mother was still living at that point. As for Judge Donnelly, she mentioned that she was married. Another point is that Judge Donnelly did know about Kathleen's DUI arrest and 'cover up'.
Elliot and Kathy also had a daughter named Elizabeth (although, granted, that name is very commonly used). Kathy was blonde like Judge Elizabeth. Elliot also visited the Judge at home regarding a case; she also represented him as his attorney when he (and Casey Novak) was sued. Now that Christopher is gone, the idea is still as wishful thinking as it was before. I'm sure also it's impossible as conflict of interest and legal issues and whatnot.