I think the start of the downfall (fans rushing away) was expecting a baby out of marriage (considering she was americas sweetheart and society sadly has this "one normal way" of living life). She was no longer seem as "the innocent virgin"
Then there was the fake marriage which again were against societies standards for an American sweetheart.
I thought these 2 events really hurt her professional name.
And her accident was sadly the nail in the coffin for her American career (which was majority of her bread and butter).