I’d thought a great deal about this back in SF when I had a good friend who, for a time, also couldn’t drink for medical reasons. Coming up with a decent substitute is a very complex problem, and as there were almost no options on the market at the time, I never came up with an effective solution and soon got distracted by something else once his course of medication completed.
Which part of a cocktail is the most important to you (and her)? Is it the raw bite of the alcohol or the conversion of an undrinkable flavor into something pleasant? A very strong and complex flavor over a short period of time? A temperature at or below the freezing point of water? The variety of options? The ritual of preparation? The inherent “specialness” of something with a built-in drinking “speed limit” (through either dosage, taste or cost)?
I don’t know of anything that can neatly and completely substitute for the mechanical, chemical, gustatory or physiological effects of ethanol. I’d started thinking that maybe focusing on one or two of those elements might possibly work.
In any case, to be a truly satisfying experience, it can’t just be a substitute. I would think it would need to be a unique experience of it’s own.