A non-owner was elected to our condo board. Is she still allowed to serve if they retroactively put her name on the title?

You are going to have to consult the bylaws for your community. Many associations allow spouses or significant others to serve on boards without being an owner, and some even allow non-related non-owners to serve. If the person was "elected" at a time when she was not qualified, possibly the election would be void, and the position would be vacant. Of course, if she later qualified, your bylaws might allow the other board members to appoint her to fill the vacancy. Without being able to read the documents for your community, that is about as far as advice can go on this forum.