[ronaldx]

I see no reason why a mitochondrial DNA test would be helpful - your point is that the mitochondria are maternally inherited?

1. Mitochondrial DNA is less apt than regular DNA to accurately identify motherhood since it has a low mutation rate.

2. The mitochondria would still come from the chimeric cells which still are a generation away from the mother's cells.

3. If you have have considered the possibility of chimerism, there are much simpler tests - e.g. the tests that they did do.

[josu]

AFAIK -and please do correct me if I am wrong - twins have the same mitochondrial DNA, therefore even if she is a chimera all her cells should share the same mitochondrial DNA.

And isn't testing for mitochondrial DNA fairly simple/cheap?

[ronaldx]

Mitochondrial DNA between twins is expected to be almost identical, but you and I also have extremely similar mitochondria: since it doesn't recombine and rarely mutates. So, you have to get to a much deeper level to identify the differences.

Even if it's now possible/cheap, that's a recent development.

mtDNA is good for finding your (maternal) ancestral group, less so for your immediate relatives.