However the idea of her having NONE of Sarah DNS is silly in of itself because the artists in Innocence Lost and Target X went out of their way to make sure Laura looked like Sarah's Mini Me. IIRC Debbie even directly points out how much Laura resembles Sarah IN DIALOGUE, so KYost themselves clearly wanted to establish such a connection.
THIS DOES NOT HAPPEN if the only genetic connection is mtDNA, which would have no bearing on Laura's appearance. If anything, Laura should most likely have come out looking like LOGAN'S mother (brunette and blue-eyed) if her only genetics come from his X chromosome (which was provided by Elizabeth Hudson).
KYost wrote that hole, Taylor was just plugging it.