Cool , I liked the dark feel of the song. It sounds like the synth worked well and followed you nicely. ?
If I was mixing this song .. I would have her come in and out some (instead of on every phrase). Your voice alone would have more impact on a lot of it.
I think I would probably use her on "just breathe" and on the bridge section both at a lower volume. I think due to the processing she is a few ms. too far behind you as well. I'd bounce the track down , slide it forward a little and check her pitch in melodyne. I think she could be improved a little with some EQ or pitch coorection. There is something a little "nervy" about her vox.
Great Job ! I could see using that on multiple tracks with different singers . I think you could build some ptetty complex harmony sections . mark