Girlfriend was attacked and injured by my friends girlfriend

To starts this happened exactly a week ago on Friday the 15th. Oregon state.

One week ago my girlfriend (we will call her K) and I plus a few other friends planned that go out to a local bar. I invited my friend (D)and his girlfriend (J) bc they were in the city for a concert. We went to the bar had a good time and drank what I’d say is a moderate amount of alcohol so no one was too drunk to remember anything as far as I am aware. On the walk home is where the altercation took place. We left at closing time which was 2:00 and it was just us four. On the walk home D said some think that K and I did not love so to say and an argument broke out between the four of us. K and I knowing D is not somebody you want to get into an argument with know his history of drinking and his willingness to fight decided to walk faster and separate ourself from them, asking them to just drop the argument and go separate ways. D and J refused and continued to follow us and insult/argue, also stating they didn’t know where they were( bc they are from out of town). D then got in K’s face insulting her causing K to push him away. J then saw this as an opportunity to grab K and throw her to the ground injuring K’s shoulder. The two scrambled in the ground as long as it took myself and D to separate the two. It is worth mentioning that as D attempted to separate J from K he attempted to kick K while she was down. Both K and I saw this. K and I not wanting to fight further rounded the next corner asking them not to follow us and went home. We got home at 2:19. I know this bc D tried to call me and I did not answer. We have not had any contact with D or J since.

The next morning K filed a report to the police of what happened. She does not wish to files charges at this time

 Not on week later with a injured shoulder( google tells us it’s separated) K upon getting advice for her doctor is going into urgent care to get it looked at and possibly get an  X-ray. 

K does not wish to pay for whatever bills result of going to urgent care and upon getting a bill we plan to reach out and ask J to cover it bc she likely caused it by throwing her to the ground.

 That is where we stand as of now. I suppose my question for you guys is how would you proceed? Any advice is welcome.

Edit: we plan to ask for the Ring camera footage from a few houses on the street that may have recordings of the incident.

Edit 2: correction this happened at 2:00 am on Saturday the 16th