She certainly doesn't need a top of the range laptop. Decide on screen size and weight - does she carry it around with her?
Battery life - does she use it mainly plugged in or does she need a long battery life?
Hard drive size - what size is her current hard drive and is it adequate?
How much do you want to spend?
Any new laptop is going to seem like a whizzy thing compared to what she is using now. Argos has decent Acer laptops for around £300 but it depends on the factors mentioned above.