Who says she isn't willing? Real life isn't like CSI, and DNA comparisons aren't completed in 60 mins or less.
I guess we'll just have to wait and see what happens with "C".
ETA: I have no knowledge of whether or not a DNA sample has been, or is scheduled to be taken from "C". However, if they are doing a test, it will take awhile to come back.
If you pay for the test out of pocket, the expected turn around time is 4-6 weeks.
Since Doogie said that LE is involved, I would expect the samples to be processed in a LE lab, which is often quite backlogged and can take several months.