My friend is a complete B**** to her dog?

Hey guys. My friend is horrible to her dog when I'm at her house. When she walks by it she'll like kick it for no reason, and she called it over to show me it's tricks and it didn't come she dragged it by the collar across the room and hit it's back like really hard. When it didn't respond to her commands shed slap it. Then later when it was streched out laying down she walked over and plopped down on his back. The dog tried to move but couldn't, I felt so bad for it, it's back must have been dying!!! My friend is like 130 pounds btw. Idk what to do, she's a really really good friend but I'm a lover of animals and it killed me to watch her do all of it. And my friend is normally like the nicest person I know. It's her house and pet, so idk what to do next time!!!?