No they're not obligated to release anything, and neither is she. In a situation like this its up to the observer to form their own opinions. People will take each parties past and future actions in account as well. It is very believable to me that LTT has a toxic culture based purely on the upload schedule and past conflict with other reviewers and product startups. I think most of the claims were descriptive enough to be believable although some may have been exaggerated and painted by the whistleblowers past experience such as the bait and switch onboarding. My opinion doesn't really matter though, im just going to stop interacting with LTT based on how theyve reacted and conducted themselves over multiple public incidents.
Generally speaking, the employer has all the power and own the records which would prove the whistleblower right or wrong and it is much more difficult to retain that information as an employee. The power imbalance in the relationship and the role of the company as custodian of records here is what changes the expectation. Power imbalance is what has caused high profile people with money and fame to get away with bad behavior for thousands of years so society is working to address that now. Not going to be perfect at first but its a good start