why is she doing this?

i was driving home from class last night. it was pretty late and my friends and i are hungry. so as we were driving pretty fast, we had to overtake a couple of cars. while we were overtaking the first car, i noticed that that car belongs to my ex-roommate, who i have no idea why, hates me. we used to be bestfriends but all of a sudden she changed and stopped talking to me. i tried asking her what is wrong but she ignored me. i even tried text messaging her while she was in the same room with me, and guess what, she ignored me, as usual.
so anyway, we reached a traffic light. my ex-friend was behind another car on the other side of my lane. when the light turned green, i started to drive but she suddenly speed up and tried to overtake me. but the thing is, the way that she was overtaking us was very dangerous. i had to use the emergency break because if i didnt step on the break we would have collided.
my friend who was sitting shot gun hurt her hand trying to stop herself from hitting the dashboard because of the sudden break. my other friend at the back hurt her shoulder because she was thrown forward. luckily, i stopped in time or not, i think we would all have been seriously injured or even died in a car crash that would not have happened if that someone would act more mature.
my friend said that maybe my crazy ex friend was angry because she thought i was tail-gating her before i overtake her.
should i report to the police? or should i just ignore someone as crazy as her?