How do I kill a screen if I know the name of it?
screen -S foo -X quit
From the man page:
-X Send the specified command to a running screen session.
...
quit Kill all windows and terminate screen.
Try using this:
screen -S foo -X kill
I would be cautious tho, depending on what you're running and the state that it's in, this may not kill the processes running in screen, and maybe cause file system instability if it has any files open (i don't know for sure, i'm just assuming)