It doesn't require the root password. It is asking you to enter the new password for the user susan (twice). And you can clearly see the message where it says password updated. That means the new password for susan now it the password you entered.
Now, if susan was the first user created on the system, it should have sudo permissions. So you should be able to use the susan user and the new password, for sudo commands.
On the other hand, if the only user that has sudo permissions is carol, then you need to use that user for running sudo commands.
After changing the password for susan, does it allow you to login with it or not?
I just simply went to a terminal window and typed "passwd" and followed the instructions ......
Simple as that