Over the top?
Technically, she could have arrested him and that might have been the end of his career.I'm sure it would have caused a big mess between departments, but the off duty cop was breaking the law.
She pulled her gun because it is out of character for a police car to be going that fast without lights or siren. For all she knew, it could have been stolen.
I'd also be willing to bet that Mr.Speedo will be disciplined for acting the fool.
And he was acting the fool. Speeding along at 120 MPH was not only reckless, but he was endangering everyone else around him. Going that fast, even with lights and siren blazing is dangerous and it takes a long time to stop.
What do you suppose would have happened if Mr. Speedo got into a wreck and killed someone? It would be a major liability for his Dept. and very, very expensive.
In my opinion,she did the right thing.