You know, it probably does have something to do with the fear of the shelter. My 9 year old step daughter had the same issue. Whatever you do, work with your dog BEFORE you have to be somewhere in 30 minutes!!!! Also, she may be more afraid of enclosed spaces, rather than of being left (would explain why she would get into the van, but not your car.) You can try opening all of the doors and just letting her explore on her own terms to get her comfortable. You can even try calling her through the car, crawl through the car with the leash and stand on one side while she’s on the other, don’t pull on the leash, just have a hold of it so she can’t run off. Have her come to you by walking through the car. Once she’s comfortable with that, have her stop and sit on her way through the car, leaving all the doors open. This may help her discover the car at her own pace. Plus, if her reward for getting into the car is that she gets to get out on the side you’re standing on, she may be more willing to endure the car for a second. WHENEVER she is in the car make sure she get LOADS of treats and loves. Take her good places like to the park or somewhere that she will enjoy so that she learns to associate the car with good things (even the vet!) However, you will also find that her confidence increases with time. As she learns to trust and love you more and more, she will be less skeptical of your request for her to climb into that box with wheels. Not to mention that, if she’s like most pits, she will overcome her unease, simply to be able to go with you, rather than be left behind. Be patient and give her lots of time. If you pressure her and yourself you will get frusterated and she will read that and pick up more stressful feelings about cars. Be persistant and she will come around.