It is great that you are willing to do this, and that people here are being so helpful. I've written before about the PITA vegan relative who we've had to accomodate for years. Like any eating disorder (something I unfortunately know a lot about, and veganism is exactly like anorexia, etc.), it consumes the person and everyone around them, and makes it really difficult to actually enjoy the meal.
I notice that a few in this thread have re-posted when they realized that one ingredient or another that they were suggesting is "off limits." What makes all this so tough is that each vegan has his/her own interpretation of what is on or off the list (some won't even eat honey because a bee is an animal).
What's worse, it changes over time. Our relative is now insisting that the food has to be whole, and won't touch things like olive oil because it has been pressed out of the plant (so-called "whole food plant based" diet).
I'm not making this stuff up.
Some vegans are reasonably accommodating, and hopefully your relative is one of those.
Some day I want to go to a vegetarian's house (they are usually somewhat reasonable compared to vegans who are, IMHO, off the deep end) and do what's been done to me dozens of times when they visit and say, "I'm sorry, I don't eat meat. Could you maybe fix a dish of just vegetables?" So what I want to do is visit their place and say, "I really can't make a meal out of just vegetables. Could you perhaps cook a hot dog for me?"
Why is that not considered acceptable, when the other way is?
Sorry I can't be more helpful on this one, but my experience is that trying to cook for these people is a losing proposition and you are far better off just asking them to bring their own meal.