My mum has a old p2 333 with a s3 virge 2mb i think gfx card and onboard sound which is probably dire to say the least.
Not at all. That's a great computer for old Win 95 games. How well it would work for DOS games would depend on what sound card it has.
I tryed grim fandango and the computer wasnt up to it.
Actually it should work in software mode. But Grim Fandango looks kind of ugly in software mode.
Amerzone would be good.
Sanitarium would be good if she's not squeamish.
King's Quest 7 (Windows version) and Dracula Resurrection have already been mentioned.
Monkey Island 3 (Curse of Monkey Island) might be a little tough for someone not used to playing adventure games.