How to retrieve data from the old Apple ID

Any purchases that she made with the previous account are the biggest problem as they are non-transferable. This would include music and movies, as well as apps. Since you mentioned that she only downloaded free apps, it shouldn't be a monetary problem. Because updates will require you to login to the old account, it would probably be better to re-download the apps with the new account. That way updates are seamless and easy.

iMessage (or SMS and MMS for that matter) shouldn't be a problem at all. All the old threads and messages should stay in tact and be usable like nothing ever changed. Call history isn't something that iCloud, or an Apple ID has anything to do with, so the change will also be without consequence there.

Yes, change Apple IDs, create a new backup and you're good to go.

Side note: iPhone actually handles Apple ID changes very easily and smoothly. Some people have two Apple IDs in general - most by accident - and they will change back and forth for app/music/movies purchases.

This is caused by a Mac AppStore Receipt residing somewhere on your system that was issued for different account. Spotlight is generally of no use in finding these, since it can't go deep enough to find them within the places they are. Usually the offending receipt can be located with a simple command, that may have to be adjusted according to your file system structure.

Open Terminal and try:

cd /

then

find . -type f -name "receipt" -exec grep -s -R -n -i "com.ensenasoft" {} \;

• Press Control - C to cancel/stop

if located you will should see something such as:

Binary file Applications/Mahjong Deluxe Free.app/Contents/_MASReceipt/receipt matches

If it failed to locate anything you will need to adjust the path, for example to search a different volume:

cd /Volumes/<Name of Volume>

then try the command again.