That is easily accomplished without a roll.
When you get to the top of the tower, Laele pulls the hood of the cloak as far down as it will go, and steps into the sun. Her body tenses somewhat and tries to pull the hood down even further, and walks in and out of the shade. Even in full light, the hood covers her face and hair well enough that you would be hard pressed to identify her as Drow, if not for your familiarity with their manner of dress.
After a few minutes, she turns to the party. “The accursed sun hurts my eyes, but I must learn to live with it, and it is not so bad if stay to the shade. I thank you for your kindness, though I think you are foolish for trusting one as I so readily, but I must leave you now.”
She addresses Dory before setting off into the woods, “I will honor our agreement Doryen, if the gods will that I live long enough, you shall hear from me again.”