What type of bra would be good for a girl who doesn't need one yet?

My best friend turns 11 in 3 weeks. She says she is too embarrassed to go to a store and buy one herself because she lives with her dad and if she were to go with her mom she would hate the women measuring her. So, she asked me to get her one for her birthday. She says she doesn't need one yet but wants to have it for when she needs one. I don't know which one to get her because even though we're the same age, I haven't bought a training bra in 3 years. What do I do?