We have a golden retriever who is a year and a half old. She refuses to get in our camper. She will jump in our truck and car. She loves to jump on furniture even though she's not allowed to. Jumping ...
I think you are right about the steps. What if you put an old carpet runner down the steps at home and have her go in and out on that with treats and fun inside when she gets in. As she gets use to it, move the carpet down a step at a time. Just a thought.