Of course it’s not her fault. Dropsy in my last 2 bettas was not my fault either, if you have a store bought betta, trust me, it’s always store’s fault.I'm sure it's not your fault. To get all of these fancy strains they have to be heavily inbred and that decreases their health and longevity. They are seen as flowers by the fish farms, you buy them, they look pretty for a couple of months and then they die and you get new ones. $$$ There is no interest or incentive to breed better quality fish (not just bettas, all species).