She's not an alto. One thing I did notice last night was that some of the singers had trouble with the low notes, and some of the songs started out low. Lisa doesn't have the sultry voice needed for Lena Horne, Katharine maybe.
You have a better ear than I do, with regard to voice placement. Lisa's voice is still very young, and it's not always good to "tag" a voice that young as limited to one particular range.
My daughter went through college as an operatic voice major, and they had her singing coloratura in all her performances. Later on, at about age 28, she was "diagnosed" by a well-known voice coach as a mezzo! What a surprise.