Although Leslie's hidden identity was extremely mysterious, Tsukihime and her companions knew of it.
Anyone closely tied to Tsukihime was someone they could easily deduce the identity of through simple reasoning.
However, Lord of Stars and War Goddess ultimately chose to remain silent.
On one hand, Leslie's identity was not definitively confirmed, and they had no solid evidence to prove it.
On the other hand, Leslie was Owen's wife!
Until Owen himself spoke about it, they had no intention of mentioning this matter.
Otherwise, once this information was revealed—whether true or false—it would inevitably shake Pure Land and the Celestial!
This would be extremely detrimental to their morale!
Most importantly, they had received word from the Celestial that the Old One had been defeated.
Leslie, too, had evidently fallen in defeat. Bringing up her identity at this time would only bring them harm, not benefit.