Are you able to upload a photo of the nail?
How wide is the stripe? Is it running horizontal or vertical across the nail?
What is the color?
Is it the nail itself or the skin under neath the nail?
Has she any history of trauma to the hand in last 6 months?
Does she take any medication?
Does it look like any of the following images:
There are a lot of nail images. I do warn you that some are not pretty!
Let me know which appears to match the best