Banks is at fault - She's been one of the top women with the company for years and knows how things work in WWE

When the 'Women's Revolution' in WWE was essentially created by Paige in response to the unfortunate nature of the 'Divas Era' in WWE. Banks, Flair, and Lynch made main roster debuts and immediately changed women's wrestling in WWE. They had already been doing so for a few years down in NXT, but things took a lot longer to change on the main roster.
Women hadn't main-evented a PPV in WWE history and weren't allowed to have matches like Hell in a Cell or an Extreme Rules match. Once those women joined the main roster, those matches happened, and during her time on the main roster, Banks had to have realized how things work on Raw and SmackDown opposed to how things go down in NXT.
People don't always have the same success on the main roster that they had in NXT, but Banks is a five-time champion on Raw. The bookers were going to have their favorites and Mr. McMahon is known to change his mind many times before signing off on some things.
While giving her the news of dropping the titles and a split from Bayley on the same day was likely not the best decision, she had to have known that it was a possibility regardless of what she wanted to do with the belts.