Upstairs there was nothing Marian could do, but she refused to shriek and beg him to stop. He wouldn't have stopped anyway, so all she could do was let Will know she was still there, unbent by everything.
When Marian started singing the sheer volume she was aiming for meant that it wasn't very tuneful. But Marian didn't really care for tuneful- she just wanted to be loud.
"ROBIN HOOD, ROBIN HOOD, RIDING THROUGH THE GLEN! ROBIN HOOD, ROBIN HOOD, WITH HIS BAND OF MEN! FEARED BY THE BAD, LOVED BY THE GOOD! ROBIN HOOD, ROBIN HOOD, ROBIN HOOD!"