I had an mtDNA test done (specifically,
mtFull Sequence from FTDNA), and want to spend the extra money for her test only if it would create more value than buying a few autosomal tests for other family members.
EDIT: according to the Lead of the FTDNA mtDNA project I belong to, I've got a heteroplasmy at 8553. Quoting her email:
what's happening with "8553T" in your case is that your maternal ancestors had the mutation (we know this because you are in the subclade that is defined by this mutation) but in your mom some of the mitochondria in her egg cells mutated at that spot again....reverting back to the original (8553C). Other mitochondria in that same egg cell still had the mutated version (8553T). This condition, where your cells have both versions of a mutation is called a "heteroplasmy" and that is what you have...if you have a sister, she might have gotten this mix as well OR she might have gotten just one version. If she got one version and it was 8553T then she'd be like all the others in your group. If she got one version and it was 8553C, then any daughters she had would also be 8553C and so there would be no trace of 8553T in her descendants. At that point, we would say that 8553 had "backmutated" fully to the original version. That is why I noted in your case that the fact you had a heteroplasmy at 8553 meant that this mutation was potentially changing in your family line. That may have given you a headache, so feel free to ask more questions if it doesn't seem clear. BTW, it is this heteroplasmy that makes you appear so "different" from the others in your haplogroup so that FTDNA's algorithm reports you have no matches...but as you can see, you are not really so far from other folks.
Would this be justification for her and my sisters getting a mtDNA tests?