Idea: try cold brewing coffee and let her try it. My girlfriend has the same issue, she does 1lb of coffee to ~8 cups water. Leave it overnight, wake up in the morning and get some hot water (if you have a Zojirushi, ~175 is good for me, 195 some mornings, otherwise just leave water on a coffee burner), I usually mix 4-5oz of coffee concentrate and the rest water in a 12oz cup. She does around 2 oz in a 8oz. It has SIGNIFICANTLY less acid, which is what tears her stomach up. I know I love drip, but after about the 4th or 5th cup my stomach feels acidic.
Sometimes I feel I was made to work with liquids of all sorts. I'm a heavy conisseur of tea, pretty knowledgeable in coffee and mixed coffee drinks, and have a terrible urge to learn more alcoholic drinks. But despite being 22, it's not because I want to get wasted. The problem with espresso based drinks is very simple: the espresso and syrup itself. While I can make well over 2 dozen drinks from various methods of milk, to messing with syrups for long enough that I feel I do alchemy with them now, you still have two very definite flavors.
Now if only alcohol didn't have alcohol in it all the time T_T
She's OK with cold brew, we've tried it before.
Whether any given cup of coffee will bother her is a case-by-case thing; any given style is probably okay somewhere; it's either going to be the specific beans or roast that bothers her, or the sanitation of the equipment is not up to snuff sufficiently.
Part of her coffee problem, too, comes from being sensitive to caffeine. She doesn't like the hard fast rush she gets from coffee; she prefers the slow lift from tea. For example, hand-poured coffee never causes headaches, for whatever it's worth, but it's far too strong for her to enjoy.
Successfully sweetening and flavoring coffee depends on the sugars involved. Dextrose and sucrose based sweeteners are usually more successful than fructose and glucose. Maple syrup is excellent in coffee, honey in coffee always tastes off.
For the most part, though, aside from a little cinnamon, I don't really like flavored coffee, and usually only add enough sugar to cut the bitterness rather than to make it sweet.
If you want to practice mixology, host a party. Start with simpler recipes and start experimenting as the evening goes on and your guests are less demanding ;) . Remember: Whether professional or amateur, the best bartenders will taste but won't drink.
Because it's not made any more and the replacement does not have as positive a reputation.