yup i read that too and was like WHAT!?! it confirmed what i thought all along. i mean we practically know james potter we've got so much backstory on him, but we know next to nothing about lily potter, bar she was muggle born, female and harry's mother with red hair and green eyes.
JK's holding back details about her cos there's something huge to come. but i don't know what. most theories are that LV wanted her to join the DE's so offered her the chance, but would that really work? she's a 'mudblood' to them so i don't believe that theory.
which leaves me with...nothing. i don't have a clue why LV offered her the chance to live. i DON'T think he was in love with her somehow, he doesn't seem the sort

. so until JK finally writes it and tells us, i'm stumped as to why she'd so important to LV.