I believe Denver is the home of the Great American Quilt Factory http://www.greatamericanquilt.com and they might be a great resource for you. There is a beginner class in quilting that might be of interest and it would be worth a call or email to see if they have classes or camps for kids.
Is it quilting your neice wants to learn? I'm sure that the many quilt shops in that area have all types of classes. I visited my cousin in Denver last spring and we spent the major part of my visit going to a lot of LQSs. You didn't mention her age so maybe that's a factor.
If you can't find someone, contact me "off-Forum:" maybe via my cousin we could figure something out!
I have a neice who lives in Denver and need a sewing instructor, when she visits Calif. she sews with me but she is in love with sewing and needs to be mentored, is there an instructor who is willing to help?? thanks