Let us completely ignore the ToM scene since so many people have issues with interpreting it.

Graendal says she will not face Rand head on when he had defeated Ishamael and Rahvin.

That is a curious choice of names. Ishamael is all powerful among the chosen, with Lanfear being his only possible match. He also had full access to the TP. Yet, Rand defeated him. Why would Graendal even mention Rahvin then? Rahvin is certainly outclassed by Ishamael. So mentioning him, on the face of it, makes no sense.

Especially given than Rand has, by this time, beaten Aginor and Lanfear as well!

When I thought about this, there is one and only one possible reason why Graendal mentioned Ishy and Rahvin: These were the only two Foresaken deaths she could lay at Rand's feet for certain. She has no real clue how Aginor died, and Lanfear's death is a mystery for her too.

This means that all Graendal is saying is that if two of the Foresaken were defeated by Rand, one of them the most powerful of them, she sees no point fighting him head-on. For the rest, she knows he was around, but has no way of knowing if he was the one to kill them.

Taking any more out of this statement makes no sense at all. If Graendal intends to make Moridin her pet, Rand being able to defeat Rahvin will hardly be a matter of concern to her. And if Moridin has to be her pet, he has to be alive, for which she has to defeat him head on...

As for when she said Sammael would kill her... she knew he held the source, and would feel it the moment she reached for saidar. By the time she was ready, Sammael would have killed her. The fact that she uses this and this alone as a reason to not attack Sammael makes it clear that in normal circumstances where both held the source, there would be a more even fight.