Agree with the others.
But I would also add to forget
about the barrels right now. Honestly. Just simply work on circles, circles, circles, and more circles (*without a barrel around*). Making sure she gives her nose and give to the bit because she is fighting you right now (throwing her nose and not giving). Making sure she keeps her hind end down and doesn't swing it around. I had to work on the exact same thing with Red (and still continually do). He has a tendency to swing his butt around because he is front end heavy, and I've gotta watch him on it.
Not saying you need to quit barrels or anything, but maybe just put them away for a week or two and just simply work on circles with her. Get her confidence up on doing the circles correctly with little "nagging"
from you. Do big circles and small circles, and spirals, and everything else you can think of. With correct practice, she should start to "self hold" herself in position. It's a nice thing I use to fall back on with Red too when he gets himself out of position. I just remind him "hey! You are supposed to have your body here please."
Now I am sure we've discussed this before and I just can't remember .... you have had Squiggy's teeth checked, right?
I'll have to maybe get a new video up on Red. I'll show you what I do to keep him soft/supple and responding to his bit, since him and Squiggy seem to be very similar in many ways. Now I did have some help because I took him to a reining trainer back in April, but I am so glad I did take him because it made a world of difference with his softness in the bridle and his circles too.
Squiggy is coming along, she really is!! But I think we need to address the issue of her resistance to the bit. There should be zero head/nose throwing. If you can get her softer i nthe bridle, he headset will automatically lower too. German martingales are a fantastic tool to use, but you don't want to have to rely on one.