I like the Sasha is Summer theory. From what I can tell, the eyes are the same color, Sasha's hair is obviously bleached, and we have the scar. We don't know what happened to summer, but imo if she is alive she would likely have a scar. My head canon is that something tragic happened to summer, during a struggle or escape she got cut in the face. In an attempt to hide her identity from her would be pursuers she dyes her hair, and changes her name. but what do I know, I'm just some dude with internet access.
Side note, the only thing that could put a damper in this theory is the mole, which I guess could be covered with makeup. Another important thing is we don't know anything about Summer's parents, depending on how rich o influential this could explain why Summer would be put in a tragic circumstance, and another reason why she would need to changer her identity. Other than that the facial structure is fairly similar, although I could be over thinking this. That's what I get for playing through LA Noire like twice a year.