I work as a publicity manager at an independent bookstore. I used to manage an annex of the store full-time, but I'm in grad school, so I asked to drop to part-time. I still help co-manage the annex while juggling the publicity responsibilities (which I felt would have been a full-time job on its own anyway; my boss disagreed). 

My boss intermittently asks me for technical help with personal things -how to back up her iPhone, restoring her iPhone, etc. These don't have anything to do with the business, and I don't enjoy doing them. How can I either ask her to stop asking me to do those things (even though my predecessor in the publicity position did them for her anyway), or ask her to pay me more than my usual rate (which is waaaaay less than I would make doing tech support anywhere else) for when she asks me to do them?

I left my previous job doing tech support because I don't enjoy it, but I feel like asking for more money might indicate to her that I do have a valuable skill set worth more than I'm being paid right now (for publicity duties that include those skills, even if they're not "tech support").