Hmm. Interesting indeed.
What's the rest of her body language doing when she does that? Is she pinning ears? Is she turning her head around, as if to bite?
When is she not wanting to go forward? Why?
Mostly I'm getting at here first is if she's uncomfortable or in pain from something. Horses are odd animals and will lash out in varying ways from pain (if that's the culprit). Any recent dentist, chiro, or farrier checks?
If she's fine there, then it's a matter of she's throwing a tantrum and needs to be made to work. What if you carrying a crop to smack her leg with when she tries to kick? (May need a crop in each hand and a lot of coordination!!!) THen you are not punishing her with a leg cue of any sort, since she's fairly light that way, but still getting your point across that its not acceptable.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.