Always have the System Restore enabled. I'm work in IT and it has saved me numerous reinstalls and even 4 hour virus-removing.
But be careful when you have the computer in domain, it may "forget" trust after system restore.
Well, check if you have all the latest videocard drivers. Or simply just over-install them.
Check all the windows updates also, clean your temp folders and see if there aren't too many stuff in the windows start-up programs list.
Yeah, it's most likely a profile error. Login with admin account, rename her profile to name.old or something and let her login from the computer A. The profile will then be created from scratch and check if this fixes the problem. Let me know!