I was thinking about this pony (mab's) today, along with the Monty video.
Mab, if she will let you groom her and put your arms round her and is genuinely happy in her body language for you to do that, I think you need to get a headcollar on her asap. Without seeing her (caveat), it doesn't sound like she's afraid of you and the headcollar - she's just knocking a rise out of you. THis is why learning to read her body language is important - if she is genuinely afraid of the headcollar, the strategy is quite different to if she's got your measure and is working you
This isn't a criticism, by the way, so let me explain my thinking. Let me also explain that Smokey got my measure about 2 months after I got him - and he was well in control
One of the things that Parelli tells you early doors is "that in horseland, whoever causes the other's feet to move is dominant". So one of the early lessons is that you don't move your feet - you cause your horse to move his. In the Monty video, he tells us that it's who CONTROLS the footfall that's important - so it's not important for you to stand still to move the horse but you have to be in control of your horse's feet. Now, some folk will be reading this and thinking "has she just got this?" and will see it as self-evident.
Your pony will allow you to groom her and pet her ON HER TERMS. When she gets fed up, she can walk away. You can walk after her but who's controlling whose footfall? She is controlling yours. That's why I think you need to get a headcollar on her so that YOU can control the footfall. I'd recommend a rope horseman's halter - don't buy a Parelli one, they are hugely expensive - you can get the same thing much cheaper, but do invest in a 12ft rope line. It's a wonderful tool.
Once you have her in the halter and line, you can start to move her around. I like to play a game with Smokey and Bugsy called "I'll groom you without moving my feet" which is just what it says. I stand in one place and move them around to groom them, pick out their feet and so on. It give a purpose to the movement and the ponies understand purpose. We haven't quite sussed it all yet but it's fun working it out together - since you have to do the job, you might as well make it a constructive learning experience for both of you.