Are we in Texas?
Been mentioned up thread but SRO should file charges on his / her own accord unless you tell them your son is unwilling to cooperate with the investigation / case. Even better that way so your so can say he had nothing to do with it - in case he’s worried about being labeled a snitch or something. Out of his control.
Very unlikely this makes it to trial stage, so don’t sweat your son having to testify in court. Ask the prosecutor to demand restitution as a part of any plea bargain so you can recoup medical expenses / copay. And I would demand to see the video. Let them redact the juvenile faces etc.. don’t hesitate to escalate to superintendent level.
It’s one thing to get shoulder-checked Derka style in the hall while passing but to randomly push a kid down a flight of stairs? Nope.
I bet this girl has a severely dysfunctional home life. It’s easy to just say fuck that little bitch etc but in reality, it’s quite sad. Try to take pity on her for likely being raised by shitty parent(s).