Hi LoveCWoman,
I think your best bet is to call the venue beforehand. In some venues, bringing gifts for the performers is no big deal; in others it's a bit more difficult to do. Let me refer you to a previous post on this topic that might answer some of your questions:
http://celticwomanforum.com/index.php?topic=4118.0All in all, I'm sure the ladies would be very happy to receive flowers from a young fan.
They are very gracious and thankful for their fans' support and tokens of that support never go unnappreciated, but you still might want to double check with the venue before you go nevertheless.
Hope you have a great time!