You’re missing the point. The Mitochondrial Eve hypothesis does not state that she’s the first human female. It states that all humans living today are descendants of this particular female. She may very well have had plenty of cousins or siblings that were all equally human, but they bred less prolifically and their progeny has died out.
Shows the power of mathematics.
Still, all of this mtDNA analysis is under the cloud of discoveries that every now and then some mtDNA from the father gets in there and does stuff!
The Sa'ami ancestry of the Iroquois, Cherokee, Ojibway/Chippewa, Berbers, Fulbe, Yakuts/Sakha and the Sa'ami was demonstrated with such a mtDNA sequence referred to by some as "the X factor". This sequence is dated back about 9,000 years ~ at the end of the Younger Dryas. Not all Sa'ami have this sequence ~ there are others.