Apple id password 2FA

Re: “… She's the only apple user in our family …”

???

Thats generally not normal; an AppleID can’t be created for a child (generally <13) without an Adult Family Organizer.

Since she’s either >13 - or her age misrepresented - AND the needed credentials remain unknown, she’ll need to embark on Account Recovery at https://iforgot.apple.com/

If that proves unsuccessful, you (the original purchaser) will need to provide proof of your original purchase to Apple via an Activation Lock Support Request to release the device’s Activation Lock which has been encountered.

https://al-support.apple.com/#/additional-support

Best of luck.

Going forward, these articles might be helpful:

Set up Family Sharing - Apple Support

Create an Apple ID for your child - Apple Support

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

Two-factor authentication for Apple ID - Apple Support

Get a verification code and sign in with two-factor authentication - Apple Support

That certainly explains it.

Unfortunately, few teenagers (and often too few adults) have the life experiences think-thru the “what-ifs” when setting-up “shiny and new” - but highly secure - devices specifically designed to keep non-users “Out.”

Hopefully, you’ll be successful in your endeavors.