I guess people behave differently in different circumstances. As someone pointed out, getting slapped by a girl out of nowhere is another thing, being called a orphan on your face and being said that your friend is using you just to get attention is another, and a bigger deal. And it's not like she has known and trusted Misha since years! She only met her yesterday .. and the first impression didn't go too well either. So she is kinda justified in what she did. Feeling betrayed and useless and all. I reckon even I would have cried if I was in her place ...
I think she would redeem herself and come across stronger than earlier in the coming episodes. And I think she was needed alone in the middle of the night, too.