wife’s secret fantasy

my wife and I have a pretty active sex life and have had a few non-vanilla exploits here and there. When we have sex, she rarely gets off without the aid of her vibrator while I penetrate her.

Recently, as I was face down in the bed she climbed in my back and thrusted her hips like she was fucking me. She playfully told me that she has a fantasy when we have sex but that it is hers and she won’t tell me what it is. I can only presume it is her pegging someone (a celebrity or someone we know? A man or a woman).

We have all the toys. We’ve tried pegging but it’s been years and she doesn’t want to try again.
I’m a little lost: why can’t I be a part of this? Why can’t we peruse her fantasy?