Resetting an AppleID password when you don't have access to an IOS device
Have her put the SIM card of the iPhone 7 into the iPhone 4s and then when the 4s asks her for the code, she can say "Didn't receive code" and then chose the option "Text me" and it will text her the code if that number is her trusted number and if the number is still active.

Then she can put that trusted number into her iPhone 4s. Once she does that she needs to go to www.appleid.apple.com and then sign into her account and then add a new trusted number. Also make sure that she is really signed into iCLoud on her Mac. You can click on the Apple Logo -> System Preferences -> iCloud and then see if it asks her to sign in or enter her password. If not, then she is signed in.

If she is in the setup process, she needs to setup the iPhone as new (Apps &amp; Data screen), and then when it asks her to sign in, DON'T SIGN IN. Choose below it "Forgot password or don't have an Apple ID?". On the next page choose "Setup Later in Settings" and it will let her setup the iPhone without an Apple ID so she can get the code she needs.

Let me know if you have any questions!