IRC 121 exclusion for joint ownership of undivided co-op share

[asgk]

Here is the situation. A mother and a daughter, together, own undivided shares in a cooperative apartment in New York City. The shares were sold. The daughter meets all requirements of IRC 121 but the mother does not. The gains on the sale are under $250,000. Since it is jointly owned, but the ownership is undivided, how does this impact what can be excluded under IRC 121?