The correct answer is B) may be in danger of being overrun by her tow. When a tug is "in irons", it means the tug has lost steerage and control, and is in danger of being overtaken or overrun by its tow. This is a dangerous situation that requires immediate action by the tug operator to regain control, such as paying out more towline (option D) or taking other measures. The other options are incorrect - A) is not the situation of being "in irons", C) refers to a tug being in dry dock, and D) is a potential remedy for the "in irons" situation, not the definition of the term itself.