The Harriot Lane immediately fired on the Nashville.
Not the case. Harriot Lane fired a shot across her bow. A common practice in the navies of the world to get a ship to stop. She did not fire at Nashville.
A couple of points. "Firing at" and "across the bow" can mean the same thing depending on how close that shot gets. The Star of the West got a shot across it's bow too. I think one of them went through it's sail. :)
Secondly, why would it have been the business of the Harriet Lane to stop any ship? Northern revenue laws no longer applied, nor did their authority to stop anyone.
In any case, Gran Tornio, I hope you can regard this as confirmation that the Harriet Lane fired a cannon shot in the general direction of the Nashville near the entrance to Charleston Harbor, and it was likely this incident that triggered Beauregard's attack on Sumter.