Depends what she's referring to. They do safety tests on various sites once a month and I've never seen a consistent leader, they change as they each adapt their engines to suit the newest threats.

Put it this way, I look after about 20 PCs for friends and family, and only my mum has ever managed to get her machine infected when she clicked on an advert she shouldn't've clicked on. Which, to be honest, is user error.

I maintain that if you're sensible with a PC and don't do anything dubious with it, you could get away without AV...

If you don't want to use MSE, I'd try Avast. But it's a bit more resource hungry, and every 12months you have to play a game of "hunt the link to the free version" on their registration e-mail...