According to all the reports, the lorry was heading in the direction the camera is facing and making a left turn off Camden High St onto Delancy St here: http://goo.gl/maps/MYWgy
The cyclist was on the right of the lorry, trying to go straight on.
There are three 'straight on' lanes to the right of the 'left turn' lane. It's entirely possible that she was in an seperate lane to the truck and was just trying to go straight on in lane 2 when the lorry swung from lane 1 into lane 2 in order to get around the corner. so it's not her 'overtaking' a lorry at a junction, but a lorry changing lanes without any warning. And that's assuming that she was going as fast as the truck, she may well have been undertaken by it right before the collision.
edit: Slow typing, lots of the above has already been said.