tell your mom to call your friends parents and then they can have a conversation about motherly concerns and blah blah blah, but it works with my mom! she just needs to have a heart to heart talk with other mothers who can understand her concerns. good luck!
oh, another thing is that it may take a little while for her to trust you completely. when i began to ride my bike alone, i started small and gradually progressed. but a half mile is not far at all........
ps--a half mile