That depends jumper, I couldn't tell you if it is resistance just from a description. If she is not moving straight, and over her back into a consistant contact, there is a good chance it is either resistance, tension or a symptom of crookedness. Most horses will show some crookedness, it may show as the tongue coming out one side of the mouth, a tilt or twist of the poll, a short stepping hind leg etc. Often these symptoms will be combined, and even more often, they are not picked up by someone other than a good, experienced pair of eyes on the ground that is clued in enough to pick up these subtle signs.
This is why these types of rules are difficult. There is no clear cut yes or no answer in the introduction of these 'blanket' rules. Simililar to the proposed blood rule that was in the media recently, the FEI trying to allow some blood to be evident on a horse at the time of competition. How on earth was that meant to be policed? How much blood can be present? Is it allowed to be flowing? How sore is too sore for the horse to be allowed to continue competing?
Dressage has so many variables as it is, to introduced more of these kinds of rules is going to turn it into an impossibly complicated sport.