Any reason not to doubt her?
Yes. She stood up and was named. We know that she said it. The anonymous source within Likud is skulking in the shadows, saying what he/she/it wants without consequences. I am sorry you still believe anything that Bibi says. But at least don’t uncritically believe anonymous messages from within his party. Was this a message from Bibi at his request? From some faction alligned with Bibi but not at his request? Some faction in opposition to Bibi? Nobody knows what this means, or who said it. Therefore, it has no credibility.
Also, Naftali Bennett said the very same thing and worse, that Bibi was promising Lapid a left-leaning, defeatist coalition. I have no inside information, but I figured out the same thing just from news reports, and repeatedly posted my conclusion. This latest bit of Likud cowardice is just icing on the cake.