How do I get Sophia out of her cell?

Hint 1 of 5:

You need to get the guard out of the way first.  See the previous question.

Hint 2 of 5:

You will also have to get past the sentry room's double doors, so you
can meet with Sophia face to face.

Hint 3 of 5:

Talk to Sophia and look at some of the choices.  If you had a rock to
hold open the door, you could let her out.

Hint 4 of 5:

There isn't a rock, but there's something about the right size to hold open
the door.  Have you taken care of the broken statue (in the canal) yet?

Hint 5 of 5:

Once you do, there will be a new item that you can take.