A few suggestions:

Try changing the properties of the installer file so it runs as administrator (right click, properties, compatibility - I think)

Or simply try right click and select run as administrator

Epson also has Windows 7 drivers that are Vista compatible. Only an 11 MB download.

Make sure she's got the correct 64-bit or 32-bit driver for whatever version of Vista.

http://www.epson.com/cgi-bin/Store/support/supDetail.jsp?oid=90754&prodoid=63069457&BV_UseBVCookie=yes&infoType=Downloads&platform=Windows&x=21&y=8