Thanks for getting in touch!
Your daughter has probably signed up via Facebook. The number you see is her Facebook ID.
If you are not sure which one to remove, you could try to remove one. If it's the wrong one then you can simply reissue an invitation and your daughter will only have to accept the invitation. She won't lose any music or playlists but she might have to re-download any songs she has saved for Offline use.
Hope this answers your question. Let us know if you have further questions.
Have a nice day!