Facts: grad student living abroad, off dad's money for a while paying my way in parts

Situation: a good female friend of mine owes me 50$, which she flat out says she cannot return. She says she's overdrawn. I say you can return it later. She says no I won't, I got you 150$ off on your flight tickets. Which she did. Part of my close friend circle, situation was not apt to make it a big deal so I didn't. The tickets I got were cheaper because she recommended a particular travel agent. But it's not cool that she did that as something for a friend and then decides not to give me money. This is a half rant half advice sought. I'm really pissed at how little space I have to maneuver. Close group and this is unlike her. Beats me why she's doing this. My gut instinct is to get pissed, but there may be more at stake.