Well, aside from the fact that this is likely some form of malware, I'd say it's a good thing. Internet Explorer is a rampaging security hazard, and really should be used as sparingly as possible; not using it at all being even better.
I would start with the usual virus and spyware scans, and odds are that will clear it up. Then set her up with Firefox or Opera or something other than Internet Explorer to use, and impress upon her the importance of avoiding Internet Explorer unless she wants to have numerous repeat sessions of problems like this or worse.
Also, if she's running Vista Home Premium and has integrated graphics, I would suggest that you suggest to her to get at least another 1GB of RAM for her system, 2GB would be even better if her system will support that much. She will undoubtedly see a huge improvement in the overall performance of the system if she does that. I can't tell if that's a desktop or laptop from just the model number, but if it's a desktop, and it has an open PCI-E slot, getting some cheap video card with its own dedicated memory would also likely provide a boost to performance. The RAM would be the big one though, the video card could be put off for another day if it's a desktop. If it's a laptop, she's stuck with what she has, so no point even bringing the issue up.
specs for sony model vgn-n320e/b
vista home premium sp1