Based on the third picture where it shows the scene of the accident, there is no sign that says "No U-turn" there. So in that sense, she is not wrong to do a U-turn there. Of course, on the contrary, one could also say that there is NO sign that says "U-turn allowed" there also. So that's my first thought.
My second thought is, if distance was ensured and speed was kept safe, no accident would occur but then again, I believe everyone knows that too. So it's just a repeated reminder.
Anyway, hope things could be settled accordingly.