If you’re really looking for a way to add flavor to just plain cream and serve it as a liquid additive to a cup of coffee - I don’t see the point. Doing that is no different from adding cream and a flavor shot separately. The only outcome I can see is that the flavor would be rather underwhelming coming from the cream only.
If it’s a flavored whipped cream, I can see that adding an extra dimension to coffee with a different flavor underneath it, but it sounds like you’re really looking for just liquid cream with flavor added.
In that case, I would stick with pure extracts (no citrus - that would curdle the cream) from the baking supplies aisle. Vanilla, of course, cinnamon and almond would also be fabulous. I would add a teaspoon per cup of cream. I’ve also tried banana, which I find really good, but it’s only available as an artificial extract and so would rule it out in my book as a “fancy” party take-along.
This would add a hint of flavor to the cup of coffee, not be like a flavor shot people think of that is typical of coffee shops.
I have no idea if this is what you’re looking for. It sounds like your hostess is looking for a real cream alternative to those yicky commercial flavored creamers from the supermarket? If that’s the case, to the above 1 tsp extract, add 2 tablespoons confectioner’s (powdered) sugar. Otherwise, the just-extract and cream is a nice alternative for those who avoid sugar, and are just looking for a hint of flavor.
A special thing I like to do with my coffee at home, and serve to guests who all love it: I add 2 teaspoons vanilla extract and 1/2 teaspoon ground cinnamon on top of freshly ground coffee just before brewing (just on top of the coffee in the brewing basket). Smells amazing, and adds a hint of flavor without any added sugar. Maybe suggest this to your hostess, too?
Hope this helps.