This behavior of your filly's has got to be STOPPED, NOW, before it ESCALATES and SHE KILLS YOU WITH IT. AND SHE WILL if this is allowed to continue. You're teaching her that she can dominate you, and worse, you're also showing her that she doesn't need to respect you, or humans in general, for that matter. If this was my horse, I'd be carrying a WHIP whenever I had to lead her anywhere, and the next time she pulled this kind of ****, I'd let her HAVE IT. Put a strong stud shank on the filly's nose, and carry the whip, and the instant she tries to rear, give her some sharp jerks of the shank and a few sharp smacks with the whip on her chest and front legs. And tell her to back up in a loud, sharp voice. She needs to learn that YOU ARE THE ONE WHO'S DOMINANT HERE, NOT HER. Do YOU WANT THIS FILLY to WIND UP IN THE KILL PEN, PAL??? Because unless this behavior of hers is dealt with and corrected, THAT'S EXACTLY WHERE SHE'S HEADED. She's got to be STOPPED, as I said, before she KILLS either YOU or someone ELSE with her behavior. What she's doing isn't CUTE or FUNNY. It's DANGEROUS, and it's going to get someone KILLED. So put a stud shank on her every time you lead her anywhere from now on, and carry a whip with you. If she acts up, USE IT.
And to add..... It only takes a MILD BLOW from a horse's hoof to fracture an adult human's skull, pal. I know, because I had a friend who lost her grandfather that way when a colt he was training reared up on him and struck him in the head. She lost a beloved grandparent long before she should have. Needless to say, that colt was promptly destroyed. If you don't want your filly to meet this same fate, then you need to get off your butt and quit thinking that her behavior is cute. It's NOT.