Dude fuck his dad, he should be arrested, it wont get worse for her she is already being raped.
Sadly Kiichi my boy, it is gonna take quite a bit to convince her to testify against her dad, and you will need to get some evidence, good for you is that since she will probably keep being used for this you could get a camera and get that Shin Sone, her dad, and the other bastard all in one move.