My natural response is to really get after her but not sure what the most effective way would be,
Your first natural response was the right one. Eat her alive. What would the lead mare do if some insolent little brat tried to kick her out in a herd?
Where I differ from most people here is that I seldom use a whip. I would not want or need one here. I would start jerking the lead-rope and would not quit until she had backed up about 50 feet. Then, I would lead her forward about 10 steps, give a good jerk and say "Whoa!", face her make her stand for little bit and then make her back up about another 50 feet.
Then, every time you interact with her, make sure you have a stiff rope halter on her and push her around in a complete 360 to the right, lead her forward, make her stand and then back her up or make another 360 to the right.
Every single time you handle her, make her back up and make her move her shoulder away from you. These a powerful statements in horse language and she understands them.
I hope she has been run out with some older horses, at least yearling mares. Horses handle and train much better when they have been 'worked over' by older horses. They have been taught to 'submit'. It is the reason orphans and foals raised alone and weaned without older horses picking on them are often times a lot more difficult to train. A horse that has not learned proper herd behavior must learn it from human / horse interaction and that is a lot tougher on both.