How can I deal with the sudden loss of my dog?

I've had my dog for 14 years, and even recently she was in great health for her age. Yesterday my sister came over to pick up some food for her apartment or something, said a few words to me, and then left. I heard her screaming outside, and when I went to see what was wrong she told me my dog, Peaches, was dead. She was screaming and crying and I told her she had to take her to vet. She wouldn't let me see her, but she told me that when she was backing out she ran over her. I just held out hope that maybe she'd be okay, but soon after she left my dad called and said she was killed instantly. I'm still in shock over the whole thing, and it's especially hard because I have an extremely strained relationship with my sister. My sister is a horribly reckless driver, but I know she didn't do this on purpose. I just feel so guilty because I feel like if I hadn't been so angry at my sister I may have walked outside and Peaches would have been okay. I keep thinking about how I hadn't given her that much attention lately. She literally was the sweetest dog I've ever known. She followed me around like a shadow ever since I got her in kindergarten. I just wish I could have had a second to tell her goodbye and let her know how loved she was. My dad also keeps telling me this is the perfect opportunity to reach out to my sister, but I really don't want to at all. I don't know what to do. I just miss my dog, and I'd do anything to have just one more day with her.