Maybe I didn't explain too good but the split never mends it is always there. I think at some point she must have done some damage and it grows split that's why I am so careful when filing.
Try it, but explain to her that she may need to have it done for 6 months minimum, by having the enhancement it on it may be all that is needed to hold the nail together while it grows out.
the fact that it always happens could just be down to that nail being weak and because it's already split the split just keeps growing, some of these guys nails are the same when they DO split them, the mear fact that they have something bonded to either side of the nail, literally PULLING the two sides together is all that is needed to help it grow out...
u can try it, I would go 9 months minimum thou, allow the split to grow out, then keep enhancing it for another 2-3 months to help suport the new unsplit nail, then I would try a course of toughen up to see if u can get that nail to harden a bit and *fingers crossed* not split again