She will need a laptop with decent graphic card & shed loads of memory.
I have read Vista is very greedy with mem and recommend 2GB Min.
You could buy large LCD monitor & switch laptop to use that. Monitors are quite cheap now.
She would soon get used to using Mac but may find it restricting on software & support.
Look at Dell website for specs to give you an idea.
Also what Laptop mag on the high street may help.