Would you call the cops if you saw someone close to you beating their dog?

This morning while I was at work, my boyfriend sent me a video of my sister (we live on the same property so he saw her out our bedroom window) beating her dog. She was mad that he wouldn’t come to her when called, so she ran over and yanked him by the collar and then punched him in his body multiple times, and then drug him through the yard by his collar and then stopped once more to hit him again. In the video, when she hits him the last time you can hear him yelp. I’m absolutely horrified and I don’t know what to do. She’s admitted to me in the past that she’s beat him, and that shes cried and apologized to him. I don’t want to cause a bunch of drama but I can’t just go on with my life knowing that he’s being treated that way. Any advice would be appreciated. (I’m in washington state if that helps with resources/information suggestions)