If you wait any longer, yes, it will get harder. The key is to make the lessons short, always ending on a positive note. Make sure that the little one gets lots of scritches and loves, so that halter training is a positive thing. Go in really short steps...one day, she lets you put the halter on, fine, leave it at that...another day, she gives her head when you pull her one way, end there...make lessons no more than 10 minutes...a baby doesn't have that long of an attention span.
With Wynnie, that's what it took. Lots of positive reinforcement, and being very clear about where the boundaries lay...what she can and can't get away with. It was hard, but because we were there daily, things got better...you just have to outlast your baby! If she pulls back, keep constant pressure on the lead until she steps forward. A butt rope will help with that too. so that if she pulls back, she can't go far. Okay, here's what a butt rope is...
Tie a rope with a non-slip knot, in a circle large enough to go around her rump...the rope should go no further down than her stifle, and should reach about the middle of her back. The rope should be long enough to come through her halter, and be like another lead rope. When she pulls back, put pressure on her butt rope, as well as her lead. When she moves forward, release. She'll get the idea that it's much more comfortable to go forward and not get pressure on her rear end. After a while...(I mean about a couple of weeks), you will be able to gradually stop using the butt rope, but leave it there for a little while so that she remembers the lesson. She'll come around...I promise. Just you must keep your cool, and let her know that moving forward is better.
Kim R.