I see that you're unable to turn off Touch ID for iTunes & App Store on your daughter's iPhone 8 because the option is blocked out. I'd be happy to provide information that may help you resolve this.
Check to see if restrictions are already enabled on her iPhone: Use parental controls on your child's iPhone, iPad, and iPod touch
Hope this information helps you modify these settings.
Thank you for using Apple Support Communities.
Have a great day!