Personally I can't believe it's scenario 1 or 3. Trump may let his team speak their minds without fear of repercussions (but if he does, he needs to cut that out) but I don't see Conway doing it. She's been a loyal soldier throughout, except she did seem to disappear for a few days after the Access Hollywood tape came out. But even if she struggled with that, she never said it in public. That leaves Scenarios 2 (Trump is playing the media and Romney) or 4 (Conway has a deep, personal hate for Romney and even concern of hurting the boss aren't important.
Her comments don't seem venomous, or spiteful. I think it's likely Scenario 2. Trump is playing everyone and Conway is playing a role.
Conway was on Newt’s campaign staff in the 2012 primary. She’s been anti-Romney for a long time.
Trump publically endorsed Romney before the 5th state voted in the 2012 primary.