That’s a really good theory. Obviously she couldn’t get pregnant in a place where time is standing still. So adoption is the best bet. The only question is what prompted her to want a kid in the first place.
I think Regina found her revenge didn’t make her happy, just as her father had warned her. She probably thought a child would fill the “emptiness inside her” that she had been told the curse would create.
There’s another aspect to your question that I am curious about: Why didn’t she foresee that a child adopted from outside of Storybrooke would grow and eventually notice that time was frozen. Or did she foresee that? Did she have a plan to deal with that? I originally assumed the library was closed from the beginning, but after hearing Mr. Gold say “You closed it, back when you still had power,” I now wonder if the Storybrooke library was originally open and Regina closed it when Henry became old enough to read, so he wouldn’t get any ideas like he ultimately got from the story book. I’m anxious to see if the library is open in this episode!