A group of individual organisms that are all descended from a common ancestor is a clade. Is there a term for a group of individuals whose matrilineally descended ancestors (mothers, maternal grandmothers, maternal grandmothers' mothers, etc.) are all descended from a common ancestor?
I'm not aware of any one-word term for this. The term "common mitochondrial ancestor" is often used to refer to a shared female ancestor of a genetically related group. If you want to specify female descendants only, perhaps you could say "females sharing a common mitochondrial ancestor". I think that's about the shortest way to say it.
I don't think there is a word for that.
However, you can refer to this specific DNA sequence as being exclusively maternally inherited (such as mtDNA for example; see also mtEve). For this sequence, the classical vocabulary from the field of phylogenetics and population genetics apply nicely.