iPhone Face ID security flaw
My 10 year old kid is able to unlock my iPhone 12 using her face whereas she is not setup on my phone. We loom similar but not that similar. There is a huge age difference as well. Anyone having same issues?
this isn't unheard of with family members.
You could try setting it up again by going to Settings > Face ID & Passcode > Reset Face ID
If you don't want her to access your phone, you could require passcode to unlock your phone.
Settings > Face ID & Passcode > iPhone Unlock
Also.. Does your daughter know your iPhone passcode? If so, that is likely a big part of the problem