Changed Apple ID email sign in, now can't sign in
My suggestion is to sign out of iTunes &amp; App Stores and try to log in using the new email.  If you go to the App Store after that and her purchases are still there then you are good to go.

Settings > AppleId > Sign out

If when you attempt to login with the new email it asks you to fill out additional information then her new email is most likely a new apple id and you will not be able to use that email in the app store or iTunes and have access to what she previously purchased.

If it signs in and you have access to all her previous purchases then you are good to go.  If not then sign out again and log back in with the old apple id.

Keep in mind there are many places that you will need to change you apple id if you want to completely switch.  All are accessible in settings.  Examples are:


iCloud
iTunes &amp; App Store
Mail


I have been through several different hells regarding my apple id.  The unfortunate best advice is not to try to change your apple id to an icloud.com or me.com address.  I have two that I manage now.  I don't like it and apple is unable to fix it which I think is ridiculous.

My best advice for if she wants to change her apple id to something less cute is to start from scratch.


Create a non-apple related email address using your preferred service that is less cute (I used gmail)
Login to https://appleid.apple.com with the old cute email
In the Account section, there is an edit link
This will allow you to change the apple id email to the new email address
Perform the log out steps from above and sign back in to each of them with the new email address.