Not only was Phillip McKeon's sister Nancy was on Alice, but so was Felice Schechter who played Nancy Olson on the Facts of Life was on an epsiode of Alice.

Yep, Nancy played the role of "Kimberly" who was the daughter of Alice's boyfriend.
Felice was one of Tommy's friends who was at some party at Mel's apartment. When she was dancing with Mel, she told him that he reminded her of her grandfather.

Hard to find full episodes of Alice on YouTube. Some are there, but none of the episodes with the Nancys in them.

Nancy was also in the Thanksgiving episode, the one where they feed the orphan children. I think Corey Feldman was in it as well.