It will be hard to make that charge stick unless you completely screw yourself in court.

Reckless driving requires intent, all you have to say is that you saw an opening in heavy traffic, signalled and changed lanes. As you were changing lanes you noticed the car behind accelerating to close the gap and prevent you from moving over, but you had already committed to the lane change and felt it would be more dangerous to abort since the trailing car in the lane you were leaving was already moving forward to take your position. After you completed the lane change the car that was now behind you continued to move at a speed faster than the flow of traffic until the driver had to slam on their brakes to avoid rear ending your vehicle.

It is important to state that at the time you initiated the lane change there was sufficient room in the adjacent lane to accomodate your vehicle, and at no time was the driver of the other vehicle required to steer sideways to avoid a collision. Any avoidance maneuver required by the other driver was purely the result of that driver failing to yield in a reasonable and prudent manner and attempting to move into the blind spot of a vehicle that was obviously attempting to change lanes for the purpose of exiting the highway.

Do not even mention that the driver flipped you off, or that you returned the favor unless the other driver brings it up. If she does make sure that it is stated on record that the other driver initiated that exchange and you responded in kind because it seemed as if she was about to deliberately rear end your vehicle.

If the Fire Chief shows up and testifies the only question you need to ask him is if he was following the other car at a safe distance. His answer of course will be yes, so just point out that if he was driving at a safe distance (2 second gap) two cars back he would have to have been a minimum of 100-120 feet behind the point that the lane change was initiated with his view obstructed by the vehicle in front of him. His only perspective would have to have been that the woman braked hard to avoid a collision. He would have no way of knowing how much space was available to you, or whether or not the hard braking was a result of the other driver's failure to yield or not.

Remember that Reckless Driving is a misdemeanor so this is a criminal case and the burden of proof is on the accuser. All you need to do is raise is reasonable doubt.