I am an older guy 61 with over 30 years lifestyle experience who stays fit. I have been in several long-term sharing relationships. I have also been a 3rd joining many sharing couples for long-term relationships. I have worked a couple of newbie couples as well. At my age i am able to enjoy sex with fun couples and occasional solo females of all ages by being trustworthy and relaxed focusing on their needs first.
So here goes on how you get her interested in your fantasy; you stop focusing on your fantasy and ask here what is/are her fantasy or fantasies. Then try to deliver her vision if her fantasy is able to accomplished. If not then spend a lot of time with her fantasy, talking about it during sex. You may get a "I don't have a fantasy", which is bullshit. Keep pressing because if they don't have a fantasy persey, they will have components of what gets them excited. I had an ex partner that didn't have a complete fantasy she did have a thing for showers and having her feet washed.
Start with whatever she gives you to work on her turn-ons. After a sufficient amount of time focused on her fantasy, probably no more than 2 weeks, work in her fantasy to yours. You might have to be creative here, but I have never had two individual fantasies of couples that couldn't be joined at some level.
Pay attention to her. Smile everytime you greet her. Then create a fantasy story of your fantasy, BUT in the fantasy there should be lots of the words focused on her beauty, her body description, her sexiness in your fantasy, then thank her for being your fantasy woman. Keep up focused on her, making her feel sexy and the only women for you, then insert your fantasy.
The key to this process is 2 parts; focus on her wants and desires first (not yours,) then incorporate her fantasy into yours, then focus in how sexy she looks in your fantasy. 🤩
Learn to do sexual sex talk, trying to be creative. When in doubt use Webster Thesaurus so you avoid being repetitive.
If you want her to be your fantasy, you have to be her fantasy by making her paramount in your eyes. If you can do this you will be rewarded with a woman who "wants" to be there rather a reluctant wife "having," to be there.