Slide up from behind her and hold her. Firmly.
If she don't sigh and melt in your arms, or at the very least give you SOME sort of play with an explanation.
Loosen the hold, say that you're here when she's ready to talk
Then, fukkING. LEAVE.
Especially if she got all mad and pushed you off when you tried to hold/console her. She clearly don't wanna talk about it, or atleast not to you, so you offer her a chance to do that shyt whenever and maintain radio silence until she does and see how long it takes for her to respond. Passive aggressive shyt, I know, but if she really been having a tough day and just wants to be by herself, you should get a call within the night, the most a day or two. If she waiting for you to initiate conversation with her again, after she clearly rebuffed your attempts to talk about it...then she should be calling/texting you back all "Where you been?"
and let her know that you ain't gonna stand for moody bullshyt like that.
I hate chicks who get angry with me for that sort of shyt and STILL expect me to be behind 'em like some sort of kitten, mewling and asking what's wrong until they choose to acknowledge that shyt.
I'm here to hold you down, not fukking play bytch difusal when you get angry and look to take that shyt out on me.