Yuuki Konno in SAO

Yuuki enters SAO when she is 11 years old after getting SAO from her Kayaba's assistant (along with the medicuboid trials) as a way to try and help save other from dying like her sister did.

She was in the process of healing when a newly discovered treatment for her disease was discovered.

Her appearance would be that of herself in real life and she wouldn't look as sick.

She would start in SAO and become depressed at the overall situation, being caught in a death game nd not being able to accomplish her goal of helping people.

Eventually (around level 2), she is found by Kirito and Asuna, who help her find a new purpose and they form a sort of family/trio. Despite her and Kirito sharing similar goals, it is Asuna who helps the most and becomes her mentor/instructor.

After 2 or so years, Yuuki is well on her way of becoming as skilled as she was in ALO. In the real world, as time inside SAO increases, her condition worsens slightly because of the stress.

She'll eventually start to slowly recover again however, and eventually heal completely. It might take long. She also forms the sleeping knights once she is inside ALO.