Need Help with leading heifer!!

I bought this heifer in middle of Dec.  She was half broke to lead.  Been working with her everyday since.  We have shown her for the past two weekends and when she goes into the ring she doesnt want to lead.  At home she still throws her head around like her jaw is sore when I pull on her.  So today I went to walk her and she drops to her front knees.  She did it four times.  Have no idea what to do.  Anyone got any ideas what to do?  She not crazy.  She is a puppy dog.  We show again this weekend and I dont know if she will get in the ring and if she does what if she keeps going down her front knees.... 

I used to feed our cattle, then tie them up short and high and let them stand. Brush em, comb em, blow em...or just let her stand there. If she's not used to it, start her out for short periods two or three times a day. Start letting her stand for longer and longer. That seemed to give our cattle some manners, and they started behaving and acting like show cattle when we started doing that. That's all I got...Good luck!

Thanks!!  She is use to all that. I tie her up short and she stands there like a pro.  She will walk to her pen just fine but when I go to walk her and set her up that when she starts dropping to her front knees...

Get somebody to walk behind her and maybe that will keep her going if not then you could get them to twist her tail if she stops and starts dropping to her front knees..........and if worse comes to wrorse you could get you a lil hard hell hot shot and use it on her.....