What are your thoughts on a 26 y/o mother of 4?

It sounds very odd. People do make these things up. First of all, the only way to know if somebody was a bone marrow donor match would be to test their bone marrow (even siblings, mothers, fathers, etc are often not matches). There is no way to tell by looking. Also, 2 years is a long time to have such a severe disease as leukemia without looking very ill and having any treatment. It would be very odd for her doctors to not recommend the most aggressive treatments giving her age and having children at home. I would either approach her honestly that you think she is lying, or chose to not believe anything she says until you have more solid proof. Most likely it is just a way for her to get attention that she is lacking.