If this horse is running over you, it has no respect for you.
you first need to gain control on the ground, leading grooming feeding etc.
If you can, find someone around you that can help, it would make things easier.
if I knew more of her behaviour on the ground I may be able to help you further.
How long have you had her.
Does she, bite, Kick.
Does she push you when leading her.
can you pick her feet up, to clean out her hooves.
You will never be able to force this mare, she weighs alot more than you do.
As far as lunging her, keep her on a short lead at first, you have more control, small circles. and if you can get someone to walk her in a circle while your in the middle, may give her some idea of what you are asking.
If she keeps coming in to you, flick the rope from where you are, the end you are holding, that is connected to her halter, this may hit her chin, but it may stop her from coming in.
Remember get the walk right first, then go into the next gait.
Use verbal words like, walk on/up, trot on/up etc. to stop you may like to give a verbal command. and put you hand up.