I want to back up iPhone 7 before factory restore but don’t have passcode

Unfortunately, you can't. If you forgot the passcode, you will need to perform a reset which will wipe the phone of any data. Hopefully she made backups of her phone.

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

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

How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support

How to reset your passcode using a computer.

If you forgot your iPhone passcode - Apple Support

Earlymomma3 Said:

"I want to back up iPhone 7 before factory restore but don’t have passcode: Trying to restore my mom’s iPhone 7. She lost passcode and wants to backup the cell before factory reset. How can I recover passcode."

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Troubleshooting a Locked iPhone:

Hold it Right There!

Enter the passcode incorrectly too many times, and you'd likely be locked out for good. So, hold it right there, and refer to this link: If you Forgot the Passcode on your iPhone, or your iPhone is Disabled - Apple Support. It would be the one you've always entered. If you do not know it, then look for it in a location you may have stored it in.

No Success?

Contact Apple support:

If you cannot get the above link to work, then contact Apple Support.

Apple Contact Info:

• Contact Us - Choose Locations
• Proceed from there, as necessary
• Why the Wait: Phone calls are taking a bit to go through at the moment, due to lots of calls. With the Coronavirus Pandemic, many are at home at the moment, with much time on their hands to contact Apple. So, just stay on the line, and you will get through :)