listen, i'm 38 years old and my Mom has the exact same response. like, she actually says "NO." I've toured Greece, France, and, as a camp counselor during college, actually lead bike trips in the san juan islands, but she STILL freaks out. i'm going to do the pacific coast next month and she's apoplectic.
its just how mom's are. and if she's anything like my mom, and it sounds like she is, she'll probably be like this forever. ha!
i agree with the advice above about planning it very much out in the open and sharing every detail. maybe she can drive up and meet you like half way or something, just make make sure everything is cool.
good luck, i know you're going to have a great trip!