Trouble moving account from Fitbit to Google

My wife's Fitbit account has been difficult to move to Google. We created her account easily enough. When we tried to sign in using her Google account, it acted as though she had never had a Fitbit account, and essentially set up a whole new account for her. Her previous data disappeared, her food log vanished, and her scale wouldn't sync anymore. What happened? She's had to enter almost everything again.

She's using an iPhone 14+ with iOS 16.6 (20G75).