Yuuki enters SAO when she is 11 years old; gets SAO from her sister as a way to have fun and forget a bit about her life. She was in healing process as a newly discovered heal for her diasease was discovered. Her appearance was still be her normal diasease and she wouldn't look as sick. She would start in SAO and eventually come under the wing of Asuna, which takes care of her and makes her an apprentice. After 2 or so years, Yuuki starts to be a bonefied badass again. On the real world, as time inside SAO increases, her sister dies, and she isn't too good. 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.