[COBI]

I think it would depend. Even if they ask you, if it's something as a developing MUA you think would be good or important to add to your portfolio, then you may want to absorb the cost. However, I would also make it clear that is why you aren't charging, so that they expect you to do their makeup for free forever.

Beyond that, it is up to you to decide, if it's work (which should be paid) or a favor for a friend.