There are also "car clubs" where you borrow the car and pay per hour. Useful mainly if she lives nearby the depot.

For example:

http://www.autoshare.com/index_login.html

They have 50+ locations in Toronto, charge $6/hour, have some cool cars (Prius, Smart -- no good for me because I'm 6'2" and the proud owner of a new RX-8), and offer a 10% discount on Metropasses.

Note I have never used them so I can't vouch for how well this works or the quality of the cars. However, I do know one person that uses them regularly.