Stubborness in border collies?

Positive reinforcement with treats. if she knows she is going to get a treat when she does something good she will be more eager to do it with out a fight. You may also want to keep her on a leash. Sometimes being lead is the best way to manage a stubborn dog. But if the behavior is just annoying like the refusal to get in on the boot that is just her preference and you need to go with it. And next time she refuses to get in take her back in the house/yard, drive around the block but come back to get her. If she see's you are willing to leave without her she may just get in the the first time!