You need to do two things
- Change her Apple ID and Password to a new one.
- Invite her to become part pf your Family Sharing and allow her to do purchases, download and update using your payment details.. You can also set limits.
Family Sharing
Share your favorite things with your favorite people.
Family Sharing makes it easy for up to six family members to share iTunes, Apple Books, and App Store purchases, an Apple Music Family Subscription, an Apple News+ subscription, and an iCloud storage plan. Your family can also share a photo album, calendar, and reminders, and even help locate each others’ missing devices.
Get organized.
One adult in your household—the family organizer—chooses a feature for your family to share and invites family members to join. After the family members join, Family Sharing is set up on everyone’s devices automatically. Then if you want to add more services to share with your family, the organizer can update your Family Sharing settings at any time.
Choose a feature
Send an invite
Getting set up is simple.
You can use Family Sharing on your iPhone, iPad, or iPod touch with iOS 8 or later, your Mac with OS X Yosemite or later and iTunes 12, or your PC with iCloud for Windows.
- On your iPhone, iPad, or iPod touch, tap Settings > [your name]. Then tap Set Up Family Sharing > Get Started, then follow the onscreen steps. If you have iOS 10.2 or earlier, tap Settings > iCloud > Set Up Family Sharing, then follow the onscreen steps.
- On your Mac, go to Apple menu > System Preferences > iCloud, click Set Up Family, then follow the onscreen steps.
You can also set up Family Sharing when you sign up for an Apple Music Family Subscription, or when you buy an iCloud storage plan to share with your family.
All your family’s purchases, on all your family’s devices.
When you set up purchase sharing, the songs, albums, movies, TV shows, books, and apps purchased by family members are immediately available to everyone else in the group. And, of course, so are new purchases. The content appears automatically in the Purchased tab in iTunes, Apple Books, or the App Store for each family member. Just select the family member whose collection you’d like to browse, then download or play the content you choose. Other family members can access your collection in the same way. If you want to keep some purchases private, you can choose to hide individual items or choose not to share your purchases in your Family Sharing settings.
In-app purchases can't be shared with your family members. Learn more about the types of content you can share.
Making purchases is easy. So is setting limits.
With purchase sharing, all new iTunes, Apple Books, and App Store purchases made by your family are billed to the organizer’s account. But the organizer can still call the shots. Just turn on Ask to Buy for children in the family. When a child initiates a purchase, an alert is sent to the organizer, who can review the download and approve or decline it right from the organizer’s device. This applies to both purchases and free downloads.
They ask to buy
Before your children can make a purchase, they must ask your permission.
You reply from anywhere
A notification appears on your device. You can review the request, then approve or decline it.
Family Sharing - Apple Support
https://support.apple.com/en-us/HT201060
