IMHO, if she likes shooting anything, even if it is not blackpowder then capitalize on that.
I met a woman that wasn't into guns but loved archery. Before the day of smart phones with photos, she showed me her little pocket photo album of all sorts of big game she took with her bow. We're talking about everything from white tail deer to moose, bear, elk and Dall sheep!
She was hunting in places and taking game that 99% of us only dream about.
She loved the outdoors and was a hunting fanatic but only with a bow. She didn't hate guns but preferred something else.
What I am trying to say is that if she's into any kind of shooting, whether it is archery, airguns, modern guns or black powder then pursue that with her. You don't have to make muzzleloaders the centerpiece of your relationship.
On the other hand, if she will not entertain anything to do with hunting or shooting then dump her and move on. It will only get worse.
That's my two cents worth.