7 is quite a young age but as long as there is competent adult supervision for your daughter I can't see a problem, but as i said make sure your daughter will be accompanied and supervised at all times! If your daughter loves Gwen Stefani enough to want to go to the concert then she will already be familiar with the music so her mother/you are probably already aware of any innapropriate lyrics etc. Ultimately of course its up to you but if you are sure your daughter will be well taken care of and looked out for it could be a lot of fun for her. good luck whatever you decide!