car accident

i needed to ask a question i had an argument with my friend at her
house so i got up and i disided to leave before before the situation
got worse when i said im leaving my friend followed me out to my car
still trying to talk about the issue when i open the door of my car to
get inside she stood in side the door i told her to move so that i can
go she would not move my 2 other friends came down and was telling her
to move and let me go home so my friend slammed my door on my car and
start yelling at me and my other friends at this point im backing out
she goes and swing open my door while im backing out and my door hits
my friends car that was parked on the side of me it caused damage to my
other friends car i would like to know what steps do i take in the
situation and who's at fault you can please send me some info thanks