Betty had a virtual version of XP running within Windows 7, and suddenly it wouldn't work anymore. Leo says that the file may be corrupted and will need to be rebuilt.
The chatroom points to a tech note on how to repair Windows XP mode in Windows 7.
Here's a technote on restoring XP .bkf files.
It's also possible to mount the Data File in Windows as a virtual hard drive. Look for a VHD file. Right click on it, select "Send To". Mount the VHD. Then she can mount it inside Windows 7 and bypass XP altogether. Then she can try and get her files out from there. Another option is Media Heal.