I just adopted a female from a shelter too. She has the same fear of getting into a car and like you nothing seemed to motivate her to get in. She just recently started to get into the car on her own. We are so excited because she is 78 pounds and installing a crane to get her in the car was just not an option. The trick that seems to be working for her at this point is that getting into the car consistently means she is going to go have fun. I think it’s all about trust and consistency. Even if we have to go do something that isn’t so fun (the vet for instance) there is always something fun that happens afterwards. Unfortunately, this has been totally her idea and there was no ah-ha fail safe method of getting her into the car. I think you are just going to have to gain your dogs trust that getting in the car is how you get to have fun.