Yeah. Tell her this crazy Janeway person ordered you at the butt end of a phaser to make her shop.
I guess you want to buy the food yourself and it gets awkward to have her pick it out and you pay for it rather than it just being in the house. So maybe if you tell her, "I need you to help me shop vegan!" and then pushily purchase it all it will be okay.
We lived together when Voyager was originally airing, so she'd just take that as par for the course about the "crazy Janeway person" orders.
Definitely footing the bill though, I do want to be a gracious host but yeah... too much room to err. Oh and we already have two places we'll be going to as she loves them every time she comes into town. Shipley's Doughnuts(really) and Freebirds a kind of Tex-Mex place.