Check out an excellent guide to buying a woman's bike.
A small mountain bike is not a bad choice for a 4'10" novice rider considering the dearth of other sensible styles for small people. Beware bikes which have low standover but are meant to be ridden with long exposed seat-posts, these are built proportionately longer for their height. Your GF would most likely need a bike with a short reach from saddle to bars.
The Terry Susan-B is an excellent model, a standard, lightweight, general-purpose hybrid style bike built with 26" MTb wheels. These are highly valued in the used market but you may get lucky.
Many womens road bikes use a different 26" wheel (650c) suitable for very narrow tyres only. Avoid these for general purpose riding.
Some small bikes use large 700c wheels, Designers have to bodge the geometry and they are a real handful for small riders so avoid.
You can get smaller frames in 26" MTG wheel in the "comfort" style such as Raleigh Venture (every brand does them), these are OK for general riding around.