Depends on the relationship. If someone is treating you badly and saying nice things, it's just a "hoovering" method or manipulation to keep you around. I agree that it's not a usual expression used in romantic relationships, but not necessarily childish. I would just be cautious with this woman in every way, given the history.

Here is an article on hoovering.

7 Tips to Avoid a Holiday "Hoover" by a Narcissist | The Savvy Shrink