Follow these steps:
Create a Child Profile in Your Amazon Household
You can create up to four child profiles in your Amazon Household to choose which content is shared with your kids. Existing Amazon FreeTime and Amazon FreeTime child profiles will be automatically added to your Amazon Household.
After a child profile has been set up, it can be quickly accessed from Kindle FreeTime on your device. From Home, tap the Menu icon, then tap Kindle FreeTime.
Child profiles can only be accessed from devices that support Kindle FreeTime. Go to Using a Profile to learn more about using this feature on your device.
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Follow the second step, manage the profile on Amazon's website, then select the books to be shared. If you select none, it will show all of them. So try selecting one, then reset her kindle and go into that account again.