A female friend may appear to be upset with you, and might not be inclined to admit it. If you ask what's wrong, she'll probably say"nothing." There's nothing you can do but use your intuition, deduce what's bothering her and then try to make it up to her in some way. However, you might want to re-evaluate your friendship with this person. She's probably too uncommunicative. The term"acquaintance" might suit her better than friend.