The easiest way, if her computer has a stock setup (i.e. was installed by a computer company or someone other entity who didn't know what they were doing) is to reboot and repeatedly press the F8 key until given a menu. Choose to boot into "Safe Mode" and log into the "Administrator" account. The default XP install is to not password this account, so when you log in she could reset the password to her normal account.
If that doesn't work, PM me. There are....other ways of obtaining the password, but I'd prefer not to discuss them openly on the forum.