This could be completely wrong, but perhaps it happened here:
maps.google.co.uk/maps?q=NR27+9SW&hl=en&ll=52.929939,1.293648&spn=0.001259,0.002414&sll=52.931448,1.301866&sspn=0.040302,0.077248&t=h&hnear=NR27+9SW,+United+Kingdom&z=19&layer=c&cbll=52.929892,1.293443&panoid=gHvFlz5hlEu81wh2pJ7kzw&cbp=12,37.53,,0,7.28
?
As a cyclist I would tend to wait tbh, but it's a difficult situation really, you get some motorists who whine and moan if cyclists ride in the middle of the lane (which is where I would be in this situation), and you get others who complain if they go up your inside. So whatever you do you can't win really.
I have had situations like me situated on the right of the lane, obviously turning right, and car drivers pulling up on my left and turning right across me so I cannot turn. Basically the best option is to take control of the lane when turning, which is to sit in the middle.
Sometimes you get a situation at a T-junction where there might be say five cars ahead, some turning left and some turning right, but with insufficient room for each to get in position to turn, so you have a car turning left waiting in the queue because the lane is blocked by a right-turning car. So I'm not going to wait for this to resolve itself, I'll just make my way to the front.
In this situation (my streetview link above) there's really no sense in the cyclist jumping in front of one or two left turning cars, the potential benefit (since the cars are turning left, which is much easier/quicker than turning right) is very small relative to the extra risk and it's crap riding really. But again it's difficult to say, it could be there were more cars behind you in which case she was just continuing to pass the stationary queue, which is more logical, and to be honest, as I said, positioning yourself behind the lead car is not really risky - you are not going to get squished going up the left-side of a car that is already turning left at a T-junction
Whether or not the riding was poor or ok, it sounds like you deliberately cut them up, which is not good driving, and then perhaps cut them up at the roundabout as well?