That depends on what she really likes to do. Try to assess her about what she wants and what she is comfortable in doing. Children usually get tired if they are forced to do something they don't like.
I prefer for piano lesson, coz I love musical instrument. Even without a singer, a piano can give a multiple melody which good to our ear to listen. If you are a pianist, you can be more popular than other musician , because only few people knows how to play a piano. As far as I know, playing a piano can help you a lot to overcome stress, cos you stretch your all fingers.