Greetings,
Welcome to the forum.
I am not a HP employee.
Tip, set up a non-administator (user account) for guests to avoid future problems.
Wild card, your PC updated to Windows 10, version 1903 unsuccessfully after your granddaughter was using the PC???
I cannot find your HP PC using "24-B017c".
So, if you have tried all Windows troubleshooting options and can boot to HP diagnostics with all tests passing this suggests the operating system may be corrupt beyond repair.
Your hardware should be okay.
Check out some Windows 10 operating system recovery tips at this site (Link).
You can create bootable Windows installation media at this Microsoft site (Link).
Now boot to the media you created in the second link. Select "Repair". Additional instructions for using Windows boot media repair options when using the bootable Windows installation media can be reviewed at the first link.
You may have to reinstall Window clean using the Windows boot media created per the second link.
You will lose data doing a clean Windows installation unless you remove the HDD from your PC before you reinstall the operating system. Then connect this HDD to a different PC as a data drive or get a HDD to USB adapter. This adapter can be connected to a different PC via USB to retrieve data.
Regards