She literally waited nearly 50 years after the claimed switch, after she was in a new environment, with new people, without the people who would have most easily challenged it, to publicize her claim. This is exactly what we would expect from someone who was trying to hide a fraud.
Search for "Publicity (lack of)" in https://www.liebertpub.com/doi/10.1089/rej.2018.2167 for more details on that.
It's also perfectly reasonable to not want to be made a spectacle of. And to reconsider later. Maybe she didn't think 100 was worthy of spectacle, but 110 was; maybe 10 years or missing out on spectacle drove her to change her mind.
That seems unlikely, but we only have the one case of someone living that old vs many cases of unreported pension fraud so if we're assigning a prior to both I would say it's reasonable to assign a probability of pension fraud to be at least as high as the probability of her being truly that age.