It is not clear what exactly you did when you "migrated her software". If you just copied the Applications to the new machine's
/Applications directory, they are independent of user accounts.
You can create a new user account in System Preferences » Accounts under her name and give it administrative privileges. The problem is that this account will not contain any of her files or personal settings, it'll be like a store-bought machine (albeit with some software pre-installed). This is also where you can delete your old account (though I'd keep it for a while, just in case).
Her personal files (documents, images, etc.) can easily be moved to the new account -- the problem are the preferences for her applications.
Personal preferences and application support files are stored in
~/Library -- this is where both your old settings (mobile me etc.) and her current settings are stored.
I don't see an option here except either deleting all your old stuff (sign out of MobileMe in System Preferences » MobileMe) you might also want to clear your stored browser passwords from your keychain using
/Applications/Utilities/Keychain Access.app, your Mail accounts, your locally stored Mail attachments, etc.), or creating a new account for her, as described above. In the latter case, she'd likely have to reconfigure some applications -- depending of course on what she actually does on that machine.