Disagreeing here --head rubbing is a social behavior in horses. The dominant horse rubs on the subordinate horse (or so I’ve read/been told) --never the other way around. Watch your horse in a group --whom does she head rub on? My guess it isn’t the alpha mare (or if she is the alpha, she’s rubbing on everyone else).
It’s a pretty quick fix, and personally, I’d fix it immediately before she rubs harder or becomes more pushy toward you on the ground. I don’t think a horse should touch me unless I invite him/her to do so. Further, I don’t allow horses 'in my space" without an invitation --a lot of this comes from showing in showmanship classes --you do not want your horse being pushy in the ring, or any other time!
OK, my favorite fix from John Lyons -and I think you can find it on Youtube. This works for horses that snap at you when you saddle them, nip, rub their heads or any other “dominant” ground manners issues. We do it in a round pen first, with a halter under the bridle, lead rope over your arm, or over horse’s neck, but out of the way. You ride a bit, dismount. Start your usual unbridling --the second the horse turns and touches you, shout as loud as you can! Boo! No! and depending on your horse, flap your arms, step forward --your goal is to scare her --horses don’t like to be scared! As soon as you’ve done that, (yell) immediately go back to what you were doing --no drama, just back to what you were doing. If the horse does it again, scare her again. Lyons suggests giving them a pretty good scare (end of the world) --and they quit right like that. Of course be careful --you don’t want to send your horse into a panicked rearing, bucking, running away mode --so adjust your frightful yell/motions according to your horse.
There is a second way that might suit you better --nose rubs. It too is John Lyons technique. He says horses really don’t like to have their noses rubbed (you know, hands on either side of the nose, vigorous rubbing like nuggies.) it’s his belief that horses understand it is a non threatening gesture, but really dislike it. The second your horse starts to rub on you, give her a though and firm “nose rub” all the while saying nothing --then go back to what you were doing, no drama.
I know some people think their horse is “itchy” or “showing love” when they rub on you --but it is not acceptable --wait until your grey horse totally trashes your newly cleaned hunt coat with a good head rub right before you enter the ring – my riding buddy actually keeps a towel in her tack box to “do” head rubs since her horse is “so itchy” --I think she’s teaching a bad behavior --but each to their own.
Foxglove