From a mixing standpoint, what this forum is supposed to be about but usually strays into the song/performance/writing quality....from a mixing/production standpoint there is some work to be done, but if this is a first effort, at least you are somewhat aware of levels. EQ...your sister's voice is cutting through the mix a little too aggressively. Forgive me for not being able to distinguish tonight whether it is that she has a strong mid tone naturally to her voice and you should back off the mids a little on her track or that she has a strong high end and you should back off the highs. I heard a bit of sibilance, so I would say to pull back the ultra high frequencies on her track. Recording techniques and playing sounded a little raw, but it kind of went with the vibe of the song for the most part, except for a few key changes.
The vibe of the song. I like the tune, personally. It was raw and unfinished sounding...reminds me of something I would hear as a soundtrack to a good Sundance film, which is a high compliment. As far as producing in the music world without a good film score, there is a little work to be done, but good start man. The only thing I really did NOT like was the recording quality/playing execution of the abrupt chord changes somewhere middle/late in the song. Like the percussion program as well...fits the vibe of the song nicely.