Welcome to Connect @ismatjahan007 It’s wonderful that your sister has such a caring sibling looking out for her. ☺️ I’m sorry to hear she’s having some side effects to the hydroxyurea. If she’s recently started taking hydroxy, it can be a matter finding the sweet spot with the dosage over the next few months. If there’s great improvement seen in the blood work sometimes doctors may then adjust the prescription dosage lower to help avoid side effects but still maintain a treatment level.

It’s not unusual for blood numbers to fluctuate while on this medication though. While working to reduce the number of cancer cells, hydroxy can also have an impact on other fast growing cells such as fingernails, hair, mucosal tissue, and of course, blood cells. She may find that her numbers level out after a period of time.

There are quite a few members in the forum diagnosed with Chronic myeloid leukemia, but I’m not sure of their ages. This discussion might be a good one for you to explore with members @suzie71 and others who share their experiences with CML/treatments. More discussions can be found by typing in CML in the top search bar.

~I've had CML for 20 years and want to encourage others
https://connect.mayoclinic.org/discussion/chronic-myelogenous-leukemia-cml/
Was your sister having any particular symptoms that led to her diagnosis?
Has she discussed the nail blackening with her doctor?