I want to know what made my friend so upset
What gives you the impression your friend is upset?
She's crying and I want to know why.
Well, ask her. I can't guarantee she'll want to explain, but there's no harm in asking.
She's feeling sad and I want to know what's wrong with her.
Like I said, ask her. You seem like a caring friend, and depending on why she's upset, she might really need someone to rely on right now.