Question on the concept of mitochondrial Eve
As the Wikipedia article says:


  In human genetics, the Mitochondrial Eve (also mt-Eve, mt-MRCA) is the matrilineal most recent common ancestor (MRCA) of all currently living humans


Note the use of the words "most recent".  The mother and grandmother of the actual Mitochondrial Eve were living before Mitochondrial Eve, and thus are less recent than she is.