For me, cadence is certainly an interesting metric to have but IMO it isn't necessary. It does help me regulate myself in terms of power output on longer rides to make sure I don't burn out too early, but I was able to do that by the seat of my pants fairly well before I had a cadence capable computer. That said, you really can't beat this price for what you get:

http://www.nashbar.com/webapp/wcs/st...ssociationsCmd

Mine's been through rain and shine during the last 3 months and come out OK, and my riding partner has had the wireless speedometer version for over a year without any issues. If you or your friend are concerned with cadence being a distraction, you can always leave the cadence magnet off of the cranks initially, and add it on when she's a bit more confident riding later on. That way, she doesn't need to buy a completely new setup later, just zip tie a magnet to the crank, position it properly and go.