My Friend Kicked My Dog Down the Stairs!?

well, actually she's a friend of a friend. but anyway. I invited my friends Kyle and Maura over to help me paint and move and everything in my new house and they asked if they could bring their friend Maryah along. we were all upstairs and my Golden Retriever/Terrier Mix, Bentley was sitting at the top landing amusing himself by woofing at a spider and i guess Maryah got pissed or something because she came out of the bathroom and just kicked Bentley down the stairs! She swore up and down that it was an accident, but it takes a lot for Kyle to turn traitor on anyone and he says he saw it. so i threw her out and told her if she ever came around me again i'd call the police (mostly just to scare her). then Maura, who believes Maryah when she says it was an accident told me i was overreacting as usual and stormed out of the house. was i right to do this? should i try to sit everyone down and talk it out? and if it wasnt an accident, can i take legal action against Maryah and get her to pay for Bentley's check up?