OK, from what I know:
1. Turning left, you are at fault most of, if not all the times and even then, most likely at a 50% fault... it is good that you have at least a witness (you have the witness's info right?)
2. When turning left, you have to yeild to straight traffic, even if it means you have to stop and wait till red.
3. As for the appointment, you should have your mom write down all she can remember (in chinese if needed and then you translate or something)... draw a diagram or something relating to the scene... Any street names or objects should be in the picture... Was your mom able to take pictures of the accident scene or anything?