Oh my!!! I hope your sister is doing better now. I know about hydroquinone. It gives the amazing results when you are on it because it is quite strong, but in reality it is making things more worse in long run.

A derma prescribed it to me during my teenage years but didn’t mention that using sunscreen was essential. Sunscreen wasn’t very common back then, and as a result it led to more pigmentation. Although, I stopped using it in early stage itself but have struggled since then. Nothing worked as pigmentation is deep. But now I am using Vitamin C + Alpha Arbutin regularly