>>94658759I think Ashi decided to keep Jack in the dark about it.
After all, she did understand that if Aku was killed in the past she would have never existed. As she expressively stated.
Still, I do believe she didn't tell Jack to spare him of that pain and allow him to spend their final days together happily.
I still would have preferred it if her death had been more immediate, right after coming back to the past. I know they wanted to add drama by having her die on her wedding day, but it was a mistake. It's more logic and just as dramatic to kill her off right after Aku dies.