Heeeey, it's Lena with a bunch of characters :) Clarke is obviously the most relevant and she's had her own amnesia here ;) She's from I think 6x3 but I am fine with whatever canon point for Echo.
She'll get to know Rose quickly, too, I think since she's running the Mars bullshit from Earth. She'll give Echo a day or so to settle in before putting her to work. ;)