You are encouraging it. Stop her by giving her 3 or 4 hard jerks on the lead-rope and backing her -- pretty roughly -- up out of your space and teach her what "Whoa!" means. You need to have zone around you that she does not cone into without you asking her to. [I would not ask her to until she stays respectfully out of YOUR space for a good while.] Go to her to brush her, bush her head but do not rub it for a while, If she tries to bring her head around to you, 100% of the time, you need to jerk her lead-rope and move her gruffly away.
The one thing that gaining respect on the ground requires is for you to be 100% consistent. Horses do not understand why they can rub one time and not the next, so consistency on your part is key.
I can tell you my hard, firm rule -- The worst behavior that you accept is the very best behavior that you have any right to expect. They will always drop their behavior to that lowest level of acceptance.
Oddly enough (at least for most people to understand) is that they like you better, are more comfortable around you and accept what you want better when the relationship is one of 100% respect for you - a relationship where you make ALL of the decisions. You make them be very obedient on the ground and under saddle and they literally worship the ground you walk on. You are like a god to them.
You do not ever 'buy' their respect or loyalty with petting and treats. They hold people they can push around with disdain while they worship the people that make them mind.
I used to have people bring me their disrespectful or mean horses to me and they would invariably say something like "I don't know why he doesn't like me (or 'love' me). I have always treated him with nothing but love and petted him and gave him treats and yada, yada, yada."
Then they had the most difficult time understanding why their horse followed me around with ears up, listening and watching me and trying to do everything I asked it to do and all I did was boss the horse around when it needed to be told what to do and left it alone when it was doing the right thing. I would back them up, move them around, make them obey "Whoa!" and stand perfectly still and take no crap from them. The horse loved it and respected it and felt totally 'safe' around me. There was never a question of where they stood in the 'herd' pecking order or two -- them and me. The owners just shook their heads. If you are going to get along with horses and get a lot of enjoyment out of them rather than a constant struggle for dominance, you have to learn to start thinking 'horse' and not 'dog' or 'people'.