Depending on the tofu and your grill, you might want to reconsider how you cook it.
If it is the soft white silken tofu, you might end up sticking tofu to the grill, and the tofu will break apart and become a horrible mess. Tofu readily absorbs flavors, too, so if you cook it on a charcoal grill, assume that it will taste a lot different than if you cooked it on a gas grill. I think that tofu will be better if you don't marinate it beforehand, and use a sauce or a dip for it. Fried tofu with a dip is usually a winner, like a soy sauce dip made with soy sauce, scallions, a little garlic and ginger, and a bit of pepper. Or, you can use a sweet soy sauce and sesame seed glaze on the fried tofu. There is also various panfried tofu recipes out there, using fried tofu and cooking it with vegetables a'la stir fry or using the panfried tofu as a protein replacement in dishes. And, you can always ask your friend how she likes her tofu.