Sentencing guidelines here:
http://sentencingcoun...ine_-_Crown_Court.pdf
I would say, they would be hard pushed to prove your guilt beyond reasonable doubt, for this reason, the CPS would be unlikely to pursue this case (unless she can produce witnesses). In the event that they were to find you guilty, and they believe it was excessive self defence, they would find you to have a lower culpability. It's triable in either a magistrates or Crown Court, in any event with a category 3 assault occasioning ABH (lesser harm and lower culpability) the maximum you could get in a Crown Court is a fine of up to 75% of your weekly income and a high level community order (see the link for what this could be).