Black Screen of Death, newish MacBook, OS10

My wife's password on her MacBook would not work. Caps lock was not on. We both tried it numerous times. The suggestion came up and we typed it again and again and again. Nothing. Weirdly if we used the return to execute the command it would add additional characters to her password.

Then we rebooted using the Command R and got to a new screen where we were led to believe we'd be able to get to terminal and type in a command to reset the password. A box came up in terminal, but we couldn't type anything in it.

I tried setting a new firmware password, and that didn't work. So I tried restarting again using the Command R command. This time I got a Black Screen of Death. Totally black screen with a lock over a box. I read that one should type in the firmware password, but I couldn't type anything in the box.

I should add that our dog put his paw on the keypad just before the trouble began, but we don't know on which keys.

Anyone have any suggestions about how to get this computer back on line?