I did think that some of the examples offered in this thread were odd in that they seemed to ignore the central point. But in addition to Liza, Natalie Portman, mentioned by barberg, was above the title. In my several replies in this thread, I was specific. Did you read them before you posted? I mean, if you're going to post "I'm not sure ANY of the examples in this thread were teen headliners," you ought to have read all the replies before you post.
Susan Strasberg, whom I mentioned, was above the title.
And I think if you have top billing, or star billing even if not the first, it should count. Thus, Andrea McArdle, whom I mentioned, counts as she had first billing under the title in Annie. She was billed first, under the word Starring, even if below the title, and she was considered in the leading category in the Tonys.
Laura Benanti was below the title, given "Also starring" billing by herself, and only Richard Chamberlain was above the title, but she was Maria. I think that counts.