Hey guys! I have a dilemma that I'm not sure how to tackle, or if I can even do this in the first place.

Next month, I want to fly from Austin, TX to Mexico with my grandma, here is the problem:

We will travel together inbound to Mexico, however, I am returning alone. So my ticket will be round trip, and hers will be one-way.

How can I book both flights under a single transaction to ensure she gets the benefits from my United Mileage Club Card?