Actually Warren has never said that she won’t run. Every time she is asked answers with “I’m not running for president.” Notice the present tense of “is”. Sure, she’s not presently running, but she’s leaving the door open to changing her mind in the months ahead. If she decides to run, those past statements weren’t lies because at the time she said them she was not running.
It depends on what the meaning of "is" is.
It certainly leaves the door open for VP.