I think to myself that Josy and Tommy have a secret that has put Josy in a bind.
Maya used to be more adventurous. (Said Josy to Maya)
Don't you say sex outdoors. Please...not sex outdoors. (Said Derek to Maya)
Maya once said that she won't believe her father's lies anymore.
THEORY (Speculation)
In the flashback of EP4 we see Josy and Maya camping and how their relationship started in the tent. What if something more happened or maybe something happened on another camping trip.... What if there were more people present?
I could imagine Josy and Maya getting intimate in the woods. Tommy was somewhere nearby and was Josy's nail polish high. He hears, sees the two and interprets the situation fully come wrong. He is totally high and thinks that his sister is in danger and acts. Everything happened so fast that Josy and Maya could not react in time and Tommy hit Maya. Maya was knocked out and did not get that it was Tommy.
And now Josy is in trouble. On the one hand Maya unconscious and on the other hand Tommy, who was drugged and misjudged the situation.
Maya's father or Derek (could have told his father later) come running and maybe see another guy running away. Of course Josy is asked what happened and who did it. Josy covers for Tommy and says she doesn't know. Maya's father probably doesn't believe Josy because he is against Josy and Maya's relationship.
This would explain, for example, why Josy prevents Tommy's fun. He is always reminded of this situation. Why Josy hates Tommy.
Why Maya's father doesn't want his daughter to be with Josy. Maybe the father even suspects it was Tommy. Josy may also be not telling Maya.
At the Josy/Maya/MC picnic, Josy says she is afraid of losing them both.
What if the three meet the father and he drops the bomb?
And all this because of Josy's nail polish.