Dealing with grief

I know it's very early on to be talking about this but I just need somewhere I can vent my feelings and maybe get some advice. To give some background I've just turned 18 and I'd been living with my nan for the past 5 years due to the living arrangements there being a lot easier there than living with my mum. Yesterday I got home from college early to see there had been an accident only about 100m away from my local chemist. I saw a poor woman had collapsed and the paramedics were trying to resuscitate her. I felt so bad for the poor woman. I came back about half an hour later to see that they were still there and I immediately knew that the poor woman had died. I went home to then have two police officers stood on my doorstep, I thought they'd seen me and had come to question me. I couldn't have been more wrong. They gave me the news that woman who had collapsed in the road was in fact my own nan. It's broken me. I feel so upset, shocked, angry. My nan was only 64 so it was completely unexpected. I know things take time but I just want to feel okay again. I suffered really badly with depression in my younger teenage years. If any one has been through similar or has any kind words of wisdom it would be much appreciated.