Screen has a 🚫 on it

Prohibitory symbol

A circle with a line or slash through it means that the selected startup disk contains a Mac operating system, but it's not a macOS that your Mac can use. You should reinstall macOS on that disk.

Try booting with the option/alt key held down and see if you get a Recovery Partition option. If you do, select that.

Do you have a backup? If the above doesn't work, not knowing your year/model computer, see if you can boot into Internet Recovery. Try booting into Internet Recovery (command - option/alt - R on a restart). It is a slow process. This will install the newest OS that the computer is compatible with. Then install the OS. When the computer restarts, you can use Setup Assistant to restore your data from Time Machine.

OS X Recovery

OS X Recovery (2)

Boot to your Recovery HD (Restart and press and hold down the Command and R keys) once booted up to the

Recovery HD select Disk Utility, run First Aid on the disk until all errors are cleared. Restart your Mac.

If you successfully boot into the Recovery Partition, if you have never downloaded El Capitan using your Apple ID, you may not be able to reinstall El Capitan. Your mom may need to sign in to download El Capitan.