Warren's campaign has been widely reported to not utilize outside polling and places the least emphasis on polling out of all the candidates in the race. That's obviously an overall thematic, strategic decision for her campaign, and that's what she's referring to with her first response. The question was posed to her about the campaign doing any internal polling and she said she doesn't know, so unless you have evidence of Warren knowing of internal polling her team has conducted, calling her an outright liar is very weird, bordering on obsessive. She gets far more scrutiny than any other candidate, but that's the nature of the game, I get it. Ultimately, I don't really care that much if her Primary campaign team is doing internal polling or not. The most likely scenario to me is that her data team is probably doing internal polling and her campaign leadership is isolating her from them so as to not dilute her message or let those results creep into her mind. I see absolutely no reason to assume she's lying about knowing of internal polling unless you have some weird ax to grind against Elizabeth Warren.
Also, I think it's telling that all the top responses to that tweet calling her a pathological liar are all from people with Bernie in their twitter bios but that's none of my business