How to forgive a mother for leaving you with your sick father and little sister?

my mother left me when i was 8 yrs old. my father was 39 when he had his first heart attack. then his health went down hill from there! his diabetics took over him and he started to get lots of wounds and was going in and out of the hospital! my sister was 4 yrs old. My mother wanted nothing to do with me and my sister! she also wanted to not send any money to help take of us. my father had to fight with her to send up some money and she still didn't send up the money! now here is the thing my father just pasted away December 14th of 2010. I am now going to be 17 next month on July 18th. my mother and i and sister became 1 again. but it was a broken 1. my mother donated my daddy's body to science. she also didn't let me or my dads family morn she hid everything she did with dad from everyone!!!! now i went down and TRIED to forgive her but it didn't work out. then she cut off all outside communication from my sister and i. i had been my sisters mom sister and my fathers housekeeper and care taker. because he was sick! she started to push my sister around then my mother and i got into a BIG fight. she beat me up because i got my phone turned back on! and she chocked me then my gram got me up here to where i lived with my dad. under the circumstances that my gram not file any more papers! now she wants me to go down and she called the police and child and youth services. to re-enforce that i come down with her! now i don't know how to forgive her for EVERYTHING she put me thru! Please help me. I'm in desperate need know how to forgive her!