Shared Apple ID- want to create new one
Create a new Apple ID then add her to your account as a family member with the Family Sharing option. Any apps purchased under the original account will remain available (and paid for) in the new account. She would lose some things (account backups, for example, but her device would start backing up to iCloud on its own storage rather than using your free allotment). If you set the account up for her, you can still manage it as you'd know the login info.