Just from the scene - Ishamael creates three women from nothing in Tel'aran'rhiod, and two of them are confirmed to have been made of dreamstuff, why assume that the other was not? Also, the Myrddraal molesting her were also made of dreamstuff. It was just Ishamael trying to daunt Rand.

But, how do I know this?

Well, we've got the facts on Shai'tan's ability to capture souls from the Forsaken reincarnation discussions. Shai'tan has a limited window of time to capture the freshly deceased before they return to the soul pool, that is how balefire functions in regards to eliminating the Forsaken for good.

That means that in order for the Kari that Ishamael creates to be the real one, Shai'tan would need to have retrieved her soul when she died, many years ago. Why would he do this? The souls of Darkfriends return to the soul pool as well, we know this, among other quotes, because even Trolloc souls get returned, and they are far more tainted than any human Darkfriend's. So for Kari to be real, Shai'tan would need to deliberately capture her soul.

Why would he do this? He has no reason. Shai'tan certainly did not know she was the Dragon Reborn's mother, the role of trackers like Padan Fain was to establish where in the world the Dragon Reborn was located, and that wasn't discovered until this very year. And up to the moment where Rand seized the Eye of the World and fought off Aginor and the Trollocs at Tarwin's Gap, Ishamael still didn't know who of Rand, Perrin and Mat was the Dragon Reborn. Surely, if Shai'tan had taken Kari's soul years ago because she was the Dragon Reborn's mother, Ishamael would know that her one and only adopted son was the Dragon Reborn, which he clearly does not.

So there was no reason for Shai'tan to claim Kari's soul when she died, there is no possible way for him to retrieve a soul decades gone now, therefore there is no way that Ishamael had access to Kari's soul (not to mention no reason to believe Ishamael actually has the ability to summon the dead even if Shai'tan did have Kari's soul) therefore that was an apparition created from the Dreamworld, exactly like the other two. And as such, there is no reason to believe Kari was a Darkfriend.

So yes, it was an illusion.