Your horse does not respect you. That is what needs to change – the ear plugs are a sign of the problem, not the problem itself.
First, your horse needs to learn to submit to pressure on her poll. Try constant pressure. If she resists, use your other hand on the front of her face and gently rock her head from side to side. As soon as she gives in, keep the pressure on her poll, but give her a treat with the other hand. If she resists again, no treat and gently go back to having her lower her head to pressure.
This is done quietly, without fast movements. There should not be any stress while she is learning. But you cannot give up – she must submit and keep her head down until you allow her to raise it.
Once she has the idea, then have her lower her head to be bridled and haltered and pulling the blanket on over her head. As soon as she resists and raises her head, go right back to using the pressure on her poll. You cannot be in a hurry; she must learn to put her head down and hold her head down until you allow her to raise it. Only once she will do it without questioning or resistance, then you have created her respect in this one area.
The ear plugs will be harder since it is now an issue. Teach her to lower her head and keep it down while you stroke her ears and handle them before trying the ear plugs.