Yet ANOTHER moan

Sorry

Was after some advice from someone if poss? My partner in crime runs a building business and is currently building an extension in Warminster. The Neighbours of his clients have sent 3 nasty, angry little emails to Steve about him splashing their car and blocking their driveway. I know for a fact that it is an awkward place and steve and the delivery drivers try to get deliveries done as quick as possible and in no way purposely tries to block anyone's driveway. The angry neighbour once calmly asked them to move the lorry as she had to go somewhere and they did, and they apologised, but she didn't go anywhere.
Steve is 99% sure he didn't splash any car since her car is at the other end of the drive to where they are working but to be professional, he, okay I...replied back apologising and offering to get the car washed and suggested that should there be any problems to just see Steve on site and he can remedy it there and then. She only emailed back saying again how angry she was and how she will now be slating the business by word and mouth!!!!

I am gobsmacked. We have done all we can, we have apologised, even though we are unsure if there is anything to apologise for! And we've offered a remedy and said we will not park on her side anymore, yet she continues to be completely unreasonable. I want to go and slap her to be honest!!

How dare she? and legally I would think she cannot do that....about a splash and a blocked driveway. Isn't that slander? Damaging his businesses reputation?
I really would like to reply back to her email and say something to make her see how silly she is being and to stop her from such slander!
Or maybe I should just count to 10 and just ignore it...?
Any suggestions?