[terryb]

I'd start by pulling the brake lever, clean & grease the pivot and the fitting on the end of the cable that attaches to the lever. The cable probably needs a good lube too, but you'd want to make sure none of that lube finds its way to the pads/rotor, so I guess if it were me, I'd look online to find out how to disassemble that caliper & service it, so that I could lube the cable while it's detached from the caliper.
Cool bike! Hope you get it working for her!
Also couldn't hurt to clean the rotor with some brake cleaner.