Got these from googling autism bike riding
http://www.autismsupportnetwork.com/...ycling-8902312
http://www.buddybike.com/
http://autism.about.com/od/childrena...portsideas.htm
http://myautisminsights.blogspot.com...wandering.html
http://www.minti.com/parenting-advic...utistic-child/
http://www.autism-pdd.net/testdump/test18510.htm
http://blisstree.com/live/freedom-of...hubs_migration
http://applestars.homeschooljournal....riding-a-bike/
We've only had one Asperger's kid in 12 years and he left almost as soon as he'd learned to ride - the rather freewheeling nature of the sessions (which depend somewhat on which youngsters turn up) may have put him off, since he very much preferred a strongly structured environment and, I assume, your daughter probably needs that even more so?
Anyway, good luck and I hope the sites listed will provide you with enough info to successfully introduce your girl to cycling.