If her dad's bike fits you and is suitable for the riding you want to do - just get her to take it to a bike shop the week before you get there for a tune up and a safety check. Replace anything that needs some love [tires, chain, cables, etc..] that will be your easiest option and her dad will be happy to get freshly tuned bike back when you are done with it.
Vik's idea is much better than mine.
