emerging from a drive way and you'd have been blameless, but from a side street you will cop 50:50. Had she actually made it to the other side then you would have copped the full blame.
There is legal precedent: Leeson vs. Bevis Transport (1972), so a court will not see this any differently.
see here for more details:
http://www.motorcycle-training.f2s.com/filtering.html
see Example A.
I know its sometimes hard to see side roads, but we must expect traffic to emerge from them in queuing traffic. Rule 167, and 211 of the hwc put the duty of care on both parties. You may be able to claim from the bus driver however.. but its unlikely to be easy
Personally I wont filter when there are side roads unless I can do it at 5mph. It only takes a 2 seconds to wait until you are over the junction. In addition the bus could have swung out to turn left as you overtook. having said that I'm not perfect and do miss the odd side road, so I guess you were unlucky