If her legs were injured, several things could happen. 1, the legs are badly injured and they don't work very well (nerve damage, control problems, pain issues) but they don't get amputated, they are just bad legs. 2, they can't be saved and they are amputated badly after the injury so that the person is unable to wear prosthetics (yes I know someone in this situation), so they use a wheelchair. Wheelchair users with this type of injury can lead very active lives, and their disability doesn't limit them very much at all. 3, they are amputated well and the person can wear prosthetics. Walking with two prosthetics is totally possible but it is hard work and tough to learn.
If her back was injured, she could become a paraplegic or quadriplegic. A paraplegic has full or partial loss of sensation and intentional movement in her legs. A quad has full or partial loss in the arms and legs. Many quadriplegics can use SOME arm muscles, but not all. These disabilities come with a lot of other health and life concerns that you might consider, including muscle spasms, bowel and bladder concerns, pressure sores, and something called 'autonomic dysreflexia,' which is a pretty high-drama health problem that can occur any time. You can look all this stuff up on wikipedia. one other good site is called Disaboom, they will have loads of medical and first-hand info on paralysis and amputations.
My friend was in a truck at a stoplight and a tree fell on top of the vehicle (there was a windstorm). his friends jumped out the window but he was too tall to escape. The Fire dept showed up to remove the huge tree and use the jaws of life. It was VERY high drama because he was trapped for hours and he lost sensation in his legs. a paramedic told his mother that he would be paralyzed for life. luckily, when they pulled him out, he got feeling back pretty quickly, he had just been trapped in a tight position (bent over, head pressed against the dashboard).