Gaz, I know that junction well having lived in Wandsworth Common some years ago and driving it every day for a while. It has been 'interesting' to see the impact of the cycle lanes and the motorists approach to them when I do still venture down there. The junction is a 'mare. That should make us all more careful.
Whilst always easy in hindsight - and no guarantee any of us would actually do it if on our daily commute, I would like to think that the only safe technique for her, all things being considered, would have been a big Life Saver and get eye contact with a car BEHIND (as in before alongside) whilst making her own progress and intention to continue straight on clear.
One would hope that in an ideal world, said driver would acknowledge or wave her onwards and effectively chaperone her through the junction. May sound complicated or convoluted but the video should make my idea/intention clear? Hopefully...
Once again, no guarantee that any of us would actually do this in a real world situation and whilst not being 'wise after the event', it is what I would like to think that I would do in her shoes.
And before anyone shouts - SHE DOESNT HAVE TO SIGNAL AS SHE IS CONTINUING STRAIGHT ON - I refer to my post above; it really doesn't matter who was in the right in a collision with a large van and a cycle

Better to have not had the incident if at all possible.......
(I approach right turns at roundabouts - especially two lane ones- in a similar fashion and try and get acknowledgement from nearby cars before taking my 'rightful' road position)