You can use a different apple ID and Icloud account…it’s kind of awkward and I have issues too since I signed up for Itunes in 200x and then got a mobileMe account a few years later. As a result my itunes account is still on the old e-mail and not tied into my Icloud account.
You should be able to have her create her own iCloud account with whatever her primary email is. That will be the account that backs up her data, contacts, etc.
Then under settings you can change her Apple ID to your ID so that purchases and apps are synced.