Every wild duck has its own flavor profile, starting, as Tyler indicates, with the group it belongs to. Only I'd take it a step further than he did, because, among "inland" ducks, divers and puddle ducks have distinctly different tastes because they eat different things. The strongest flavor will be found in sea ducks, the mildest in puddle ducks that have been eating domestic grains.
And even the puddle ducks can taste differently. For example, wood ducks have a nuttiness that mallards lack.
Once you tell us what kind of duck you have, we'll also need another question answered: What do you mean by just the breast? Is it just the filets---that is, the chunks of meat, with no skin? Or did you pluck them before removing the breasts? Or do they have the bone still attached? All this, too, can seriously effect how you cook them.
All that aside, if this is your GF's first time with wild duck, I would definately go with something on the sweetish and/or fruity side. Perhaps something like:
Roast Duck Breast with Pineapple Chutney
(note: ingredients are based on 4-6 bone-in, skin-on duck breast halves (i.e., 2-3 ducks), so adjust accordingly)
2 tsp chili paste
3 tbls soy sauce
3 tbls lime juice
1 tbls honey
1/4 cup unsweetened pineapple juice
1 1/2 cups cubed pineapple
1/2 tsp lime zest
Pulp of a large lime
3/4 cup pineapple juice
1/2 tbls chopped crystallized ginger
1/2 tbls chopped jalapeno pepper
2 tbls golden raisins
1/4 cup chopped red bell pepper
1/2 cup chopped red onion
2 tbls white wine vinegar
Mix all marinade ingredienents in a large bowl or plastic bag. Add duck breasts to marinade, cover, and refrigerate for an hour.
Meanwhile, bring all the chutney ingredients to a boil in a medium saucepan over medium heat. Reduce heat to low and simmer, uncovered, until fruit is tender and the sauce has thickened, about 45 minutes, stirring occasionally.
Preheat grill (preferred) or broiler when chutney is almost done.
Grill or broil the breasts five minutes on each side, until a light crust forms, and meat inside is still slightly pink.
Slice each breast half into medallions. Fan these out on a serving plate. Spoon chutney over each serving.