Rand: Crazy or Crazily Sane??

Graendal thinks similar things to herself about Rand/Lews Therin in her own POVs, as if its something she's seen before, so unless she's lying to herself to undermine her own confidence in Rand, Semirhage is just using a damaging truth to do her dirty work.

 

I don't doubt that Semi would lie without hesitation, should it serve her purpose, but if the truth works, why wouldn't she use it?

I totally agree, I don't think you can write off what she says as a lie just because she is one of the Forsaken. She is just as likely to be telling a very damaging but accruate truth. The truth could actually be more damaging that any lie, because Rand will verify these accusations with his strange behaviour. Not that she wouldn't lie if she could think of something more damaging to say instead.