Unlock

You can't recover her password, you will need to reset her phone.

If you forgot the passcode on your iPhone, or your iPhone is disabled or unavailable -

How to reset your passcode without a computer if you have iOS 15.2 or higher.

How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support

How to reset your passcode using a computer.

If you forgot your iPhone passcode - Apple Support

A note to point out that you will need to know the Apple ID and Apple ID Password of the person who originally set up the iPhone to be able to configure the iPhone after it has been reset.