Arrow from mouse on 2033 Apple IMac desktop stays frozen

Try cleaning the optical sensor on the bottom of the mouse.

see "Peripherals" at > How to clean your Apple products - Apple Support

Reconnect the mouse with your Mac or test the mouse with another Mac if possible.

see > If you can't connect your Magic Keyboard, Magic Mouse, or Magic Trackpad to your Mac - Apple Support

Have the mouse tested at your local Apple Store or Apple Authorized Service Provider.

see "Explore Service Locations" at > Find Locations

Are the batteries fresh? If a Magic Mouse is it fully charged? Have to checked to determine if it's still connected if it's wireless?

She uses that wired USB mouse we all should have in reserve for just these occasions.

But is it connected? You can do all sorts of things to help the situation, but if Bluetooth shows no connection it's all for naught.

For emergencies like this, you should always have a wired mouse (and keyboard!) you can use to troubleshoot these issues.

I have found that turning the mouse off and on sometimes fixes this.

Have you shut down and restarted the computer?

If she can't move the mouse to the bluetooth symbol in the menu bar, she can't tell if it is connected or not.

Not all of us have a bunch of mice and keyboards laying around in their junk drawer. 8^)