Dude this sucks! Why are the people where you live so pants?!
You do no harm by parking the three cars on the road - as you don't have anywhere else to park them and you have the right as much as anyone else, besides the fact you pay 3 times as much tax!
It would make sense why the car cover was stolen though - maybe she did it?
What did the other people on the street say about you parking your cars there, did anyone else genuinely mind?
She is bang out of order though, not only has she got her own parking, she negates to use it and use the road to park all her cars and vans, blocking it up even more than your titchy Micras supposedly do!
She does sound a bit loopy - maybe she's just jealous of your awesome car collection? 
