You want to camp. She wants to stay in hotels. My suggestion is that you both compromise! Camp for a few days, then stay in a hotel and clean up (let's face it, staying really clean while tent camping is difficult, at best). You will be able to introduce her to camping and show her what you enjoy about it while allowing her the comfort of knowing that she will be rewarded with running water and flushing toilets the last few days of your trip. Who knows, perhaps she will come to love sleeping under the stars, the smell of the campfire in her clothes, snuggling in a sleeping bag for two, and sipping coffee or hot chocolate first thing int he morning. If you are used to "roughing" it, you may have to think ahead to provide her some creature comforts that you don't usually need. Especially in Yellowstone, follow safe food handling and disposal practices, be prepared to "talk her down" when she gets anxious if she is not a "nature girl" and be patient. Plan out things you want to see, activities you want to do, and plan for contingencies, like snow, rain, or extreme heat. After you introduce her to "roughing" it, enjoy a few days seeing Yellowstone while also enjoying modern conveniences. Best of Luck and have a terrific time!