This is a powerful piece of work with great potential. For me it's like those two women are different sides on the same coin. Becky could be Leah if she'd made the wrong choices or was less lucky, and vice versa. It's all about coincidence and that's perfectly illustrated by the way their lives cross each other's and are greatly affected.
Things that happen in seconds and we're not even aware of the consequenses they'll bring to people we don't even know, like Leah's baby who'll probably die without anyone knowing about it.
The characters are good, but I just felt that maybe you could try making them less obvious. At this point they seem so extremely opposite(which was your purpose ofcourse),but in a strange way that makes them a little unrealistic. I hope I'm being understood.
Also, I would totally get rid of the "Mama" line of the baby in the end. It makes it melodramatic and it's a shame because it spoils a great ending. I pictured something like an exterior shot of Leah's house, with backwards travelling or zoom out and the baby cry fading down- but that's just an idea of what I'd like to see last.
Generally, I believe it's a really powerful drama, which is a great success for such short time.
So, well done!