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 ...
If she likes her food just start feeding her in there. If she won't go in for her food just pick her up and set her down by her bowl. Easy as that before too long she will just climb in there and happily. That's the way they teach horses to get into the trailer. Just start feeding them inside they go in readily after a while.