Step 1: Modify your guest list to avoid this kind of thing in the future.
Step 2: Use is any way you’d like. The real-McCoy pesto is made with pine nuts; yours substitutes walnuts, which will give it a different, but certainly not unpleasant flavor. In fact, it is not an unusual flavor combination at all. We’ve come across a variety of recipes for walnut pestos and recipes that use walnut pesto, and, of course, the Diamond Walnut Growers yearn to have you make your own.
with traditional pesto, use yours as a pasta sauce, to season soups, to coat meats and fish for grilling, as a dipping sauce, or on an extravagantly delicious sandwich. Don’t hold back. Show your unconventional guest that you can be innovative, nay, brilliant, with her gift.