Microsoft Security Essentials
One of the questions I asked was whether she had some sort of anti-virus and/or spyware software on her computer. We ran it and it found no infections. If she did indeed have more than 300 as the bogus message said, even the worst software would find some of them.
So the first thing I want you all to know is to not trust a message in your Web browser saying you are infected. I can't think of any reason it would be valid! You definitely do need software to protect your computer. One of the surprisingly good choices is Microsoft Security Essentials. Not only does it grade well when various software is tested, it has everyone's favorite price. That's right, it's free. If you need something to protect your computer, you should definitely give it a try.