DIONE was one of the early birds in the goddess stakes. In fact she was on the scene so early that no-one else seems to have been around to make notes for posterity.
The fact that her name is a feminine form of ZEUS just adds to the confusion. She may have started off as female aspect of him — or perhaps he was spotted wearing a dress now and then and people jumped to conclusions.
As time went on, DIONE became recognized in her own right as a goddess of importance, even if her provenance was a little uncertain. This happens far more frequently than you might imagine — we could point the finger at several major deities across the globe who owe their existence to a misunderstanding or a spelling mistake.
Luckily, human creativity was standing by to fill the void with speculation. Perhaps she was a daughter of CRONUS and GAIA. Maybe OCEANUS and TETHYS were her parents. She could be an Earth Mother or perhaps one of the Ocean NYMPHS. Perhaps she was all of these things, or even none.
The only one who knows is probably ZEUS himself. He was there and, if one is to believe the very early rumors, he fancied her like crazy even if she was him. Between them they produced APHRODITE, claiming URANUS was never fit to be any sort of parent. Also that having sex with a sea foam bath is not any decent way to produce a daughter.
Now we have successfully covered this mysterious goddess by bestowing upon you the same ignorance we ourselves enjoy. You are welcome. Meanwhile DIONE went on to marry TANTALUS, making her the mother of NIOBE and PELOPS. Thank the gods they all had birth certificates.