Eclipse never existed in the timeline the books took place in.
The Jade Mountain Prophecy
Eclipse was indirectly mentioned when Darkstalker stated that he and Clearsight would have had dragonets.
The Lost Continent Prophecy
In the prologue, Clearsight thought that she would always miss the dragonets that she would have had with Darkstalker.
When Darkstalker gave Clearsight the copper bracelet, Clearsight said that she loved it. She mentioned how Eclipse would have needed it the most, and Darkstalker was surprised that she mentioned their future dragonets. He remarked to her that he thought they would choose the name Shadowhunter over Eclipse for the dragonet. Clearsight then told him that Shadowhunter would be one of their other daughters.
Before Darkstalker kills Arctic, Darkstalker and Clearsight spoke together about their dragonets. Later, Clearsight had two visions, one of which she and Darkstalker showed Vigilance their dragonets, the second of which she saw Eclipse chasing Queen Vigilance's grandson around, laughing. Vigilance had cracked a rare smile.
= Possible timeline