Thanks for replying, Shiny Rabbit. Her laptop is set up almost identical to my desktop (she's only ten, so I take control of all that!).
She had a blip with the sounds sending previously for a while, then they started working, and its stopped again now I've put Windows Live Messenger 2009 on
I'll have a good look at her laptop when I see her to make sure she hasn't downloaded something strange from a friend, I'm pretty confident she hasn't though, as I keep a close eye on her laptop activities.
Edit: No, I don't use any other MSN Messenger add-on, apart from this one.