OP:
First, my condolences on the loss of your daughter.
Since you now have resolved the Apple ID problems, and (I'll assume) that you're signed out of everything...
What you need to do is to ERASE THE ENTIRE INTERNAL DRIVE, and then start over.
To do this, you need to boot to something called "internet recovery" first.
Here are the steps to take:
1. Power down, all the way off
2. Press the power on button and immediately hold down:
Command-OPTION-R
3. You'll need your wifi password to continue
4. The internet utilities take a while to load - be patient
5. When you get to the utilities, open Disk Utility
6. Go to the "view" menu (upper left), and choose "show all devices" (this is a VERY IMPORTANT step, don't forget it)
7. In the "list on the left", the "topmost item" will be the physical drive inside.
8. Click on the drive listing, then click "erase"
9. Choose "APFS" from the list of options
10. When the erase is done (should take only a few seconds), quit Disk Utility and open the OS installer
11. I'm thinking the Apple servers are going to offer you "Big Sur". That's fine.
12. Start "clicking through". The Mac will reboot one or more times, and the screen may go dark for a minute or two with no other indications of activity. You need to be patient.
13. When the OS install is done, you should see the initial setup screen (choose your language".
14. Start working your way through. Be careful with choosing a username and password, you can't change the username later on without A LOT of trouble.
15. You DO NOT need to create an iCloud account, email account, etc. right away. You can skip these steps if you wish and come back to them later.
16. When setup is done, you should be able to see the finder...
Good luck.
(looks like you may have already discovered this on your own...)