I like the performance by the girl and the dealer. Not great, but good. The mugger was questionable.
Cinematography could've been better especially in the scenes at night.
I wasn't really feeling the story as well. I mean, it just happened and that was it. I wish the girl could've fought the temptation for her ring since like you said in the logline, it's the only thing that's left of her life. I wasn't emotionally attached at all when she gave that up. The ring became... well just a pricy ring. Now if you would've made the story a little bit longer and show her realizing that what she did was stupid and she regains it, mixed with some dialogue about her backstory, then I would've felt different.
Music was good though. And the sound design was a hit on the most part, but I think when you got to the night scenes, you just used the camera audio or something.
That's my opinion and I hope that helps. Good job putting everything together though and actually making a film!