Looking for a short women's bike to buy/rent for summer

A friend from Boston is going to be in town this summer and I'm trying to find a bike for her. She's 5'0", so the smaller the frame the better! No need for anything fancy, just a basic bike in decent repair.

Since she'll only be here late June-mid August, she's looking to either buy a cheap bike, or work out a deal to 'rent' your bike for the summer