Thalia shows up a few times in Greek mythology, as a muse and a Grace, or Charity. Thalia means blossoming.
Grace is Latin, meaning grace. It could also mean that he took Thalia from its origin with the three Graces.

Obviously, Thalia started out as a tree. Blossoming could be from her being a plant. I think it has to do with the original Thalia being a Grace.