No, it isn't. The way time works in SJ is that Jack was displaced from his original time, which is why he didn't age. From the point he was sent forward in time, everything that happened was subject to change if he were to defeat Aku in the past. And while we don't know for sure the fate of the people Jack met in the future, it's a safe bet that they would exist regardless, or maybe a different version of them.
However, Ashi's entire existence was dependent on Aku. His destruction in the past meant that not only would the circumstances of her birth not occur, but that they would NEVER occur. Thus, any variation of Ashi could not exist, and she disappears as soon as the paradox catches up to her.