Could anyone please advise me on best treatment on these nails. Also any reasons that could have caused this damage. They are very dry and cracked, been treated weekly with IBX and solar oil for the last month. Shellac has not been used and not sure when it would be ok to start using shellac again.
This seems to me as excessively buffing and scraping of the nail plate. You see how the markings have the shape of her cuticle line? Is she a picker?
Nothing really to do, as you can't restore what's missing. Just wait for the healthy ones to grow out. But that process takes time as it's usually around 6 months for the nail to be fully replaced (more like 8-10 in my case for instance)
IBX would ensure better condition and strengthen them for sure, and you can safely apply gel polish. But it probably wouldn't last, especially if it's shellac, because of the thinness of her nail plates
Just be patient and wait it out. Ask her how she got it. This screams of foul play.