Let's hope the tech support person is right, and has done the right diagnostics to get to his opinion. There can be a host of other causes, but it's impossible to say anything sensible on it without knowing some background (what happened) and what happens exactly if she tries to connect with her dial-up icon.
In fact, if it has worked and stopped working by some unknown cause, it's unlikely in my opinion that updating the driver will help. But it won't harm either, as long as it's the correct driver (which is a big caveat!).
She might begin with by reinstalling the old driver, if she has it on diskette or CD. Remove the modem from Device Manager, reboot and the New Hardware wizard will take over and ask you for the diskette or CD. It's a good practice, at least, for installing a new one.
If the computer she uses to copy the downloaded driver to diskette(s) or burn it to CD has some unzipping program (Windows XP has it build in) there's no need for her to have so. A driver, by the way, isn't necessarily an exe-file. In fact, usually it's an inf-file accompanied by a lot of others (like vxd's and dll's and reg's).
If there's space on the burned CD, however (and there surely is) she might like to add one of the free unzipping programs available. Choose (with diligence) from http://www.google.com/search?q=download+free+unzip
Note, however, that the first hit (winzip) isn't free!
But stuffit-expander is free and good, and there are others also.
Hope this helps.