9 months for knocking someone unconcious seems rather on the lenient side to me. Was it with intent? If so, i think for average sentances he got away quite lightly. Sorry that this is happening to your family, but i suppose if the boot was on the other foot (no pun intended) and she was prosecuting the boyfriend for knocking her unconscious you would probably rather hope he got what he deserved?
I suppose you cant really say that beating someone up is unacceptable, and right that wrong by beating someone up for it! Its also a bit of worry that someone you know well can just "lash out" unexpectedly
i Know none of the above is helpful to you because you are devastated at the moment, but i think it would b helpful if you were to think of it as rather than the judge was biased, that he let him off lightly