She was authorized—by you when you let her use your iPhone. Don't let others have access to your equipment.
Apple's terms of purchase in the USA are, "All Transactions are final," ( Legal - Apple Media Services - Apple section B), but check the terms for your country. Even if Apple does not outright say in a country that sales are final, they may say that refunds are only made to remedy defective or unavailable product. In other cases Apple may make limited refunds solely at their discretion and as an exception. Apple can also simply say no without having to provide a reason. I understand this can be frustrating but by using the service you agree to the terms.
- According to https://reportaproblem.apple.com/static/en-us/privacy.html , Apple uses an automated system to detect fraud. Your request may not have met the automated system’s criteria for a refund. If you feel you want to discuss a refund request with a person, try to contact an Apple representative by email —> “If you disagree with your final decision, contact dpo@apple.com “
On your device you can use Screen Time to prevent unintentional or unauthorized purchases from the App Store, in-app, and other Apple services. —> Use Screen Time to turn off in-app purchases on your iPhone or iPad - Apple Support
Also on your device, require a password for App Store and iTunes purchases —> Require a password for purchases in the App Store and other Apple services - Apple Support