Speaking from personal experience avoid the long term rental. You can usually get some really good weekly deals that give you about the same price as a long term rental but with long term rentals you have a km limit and then penalties apply If you can snag a good weekly rate you can often lock it in for up to 28 days. If you keep your car one day longer I believe they will charge you the monthly rate plus km penatlies and I when I was looking a few years ago they only gave you 100km a day and it might have even been less. I just remember that it was very dangerous to go over so I didn't.

Make sure to rent from an off airport location. I have seen the base rates be higher than airport locations sometimes but when you factore in the extra airport fees you are way ahead at off site locations.

Don't forget to make sure that she has a credit card with insurance coverage and you are good to go.