A mid-drive would be preferred for a long hill IMO. Derailleur or IGH is personal preference although an IGH means you need a front hub or mid-drive (the one exception that I'm aware of is a rear hub with IGH sold by ebikesca). Don't know where you're located, but it would be advisable (and fun) to test ride a few bikes. In general she'll need to travel up the hill at 8-10 mph with a hub motor to prevent too much battery energy being converted to heat.