A guest may avoid animal products and also need to avoid an ingredient common in vegan cooking. Nuts, soy, wheat, and sesame are familiar examples, but the person's own requirements matter more than a general list.
Ask what they can safely eat and how they need food prepared. Be honest about your kitchen and whether you can manage cross-contact. Do not promise an allergen-free meal simply because you plan to leave one ingredient out.
Retain packaging and write down what goes into sauces and toppings. If you discover an uncertainty after shopping, ask before cooking rather than quietly substituting something that looks similar.
For serious allergies or complex requirements, agreeing on a safe packaged option or a contribution from the guest may be more appropriate than improvising. Clear information is more welcoming than confident reassurance you cannot support.