Commuter Bikes For Ladies

MY flatmate is getting a bike on the cycle-to-work scheme and has no idea what she should be buying so has asked me to help her choose a bike.

Trouble is, I have no idea what sort of a bike a girl should use to ride a 20 mile round-trip everyday.

• Should she buy a gents bike and maximise the re-sale value for when she's done?
  
• What sort of bike? Hybrid or Mountain Bike (not a road bike, as the geo would be too difficult for her)
  
• Anyother suggestions ?
  Thanks all.