I am a BIG proponent of "take the lane". I do it all the time when I will be safer that way.
However, in this particular instance I did not advise taking the lane because we are talking about a narrow underpass which is a suddenly low light situation. I don't think that van driver even saw her until maybe the last second. I go under an underpass like that regularly on a busy highway near here and let me tell you it is DARK despite it being not all that long a 'tunnel'. Your eyes are used to the sun and then all of a sudden it's dark in there with more bright light up ahead in the open. You really don't want to be in the middle of the lane in a dark underpass with fast moving trucks coming up behind you.
I also don't think it's necessary to use red blinkies during midday (unless it's raining or foggy), but i did suggest it for this situation if the rider is going to be riding through that underpass. She could pull over sometime before the underpass and turn her blinkie(s) on and then turn them off again later on in a safe place.