Mothers iPhone is frozen

What happens when you tap below the icons on your screenshot?

Just to make sure, these are the official instructions to force a restart:

https://support.apple.com/en-us/HT201559

If your device has a frozen screen, doesn't respond when you touch it, or becomes stuck when you turn it on, see these instructions:

https://support.apple.com/en-us/HT201412

Rapidly press and release volume up, rapid press and release volume down button. Then press and hold side button until Apple symbol appears in screen then let go. To hard reset.

A hard reset should do the trick:

See this guide: https://support.apple.com/guide/iphone/force-restart-iphone-iph8903c3ee6/ios