I'm afraid that you seem to be grasping at straws here. The only evidence that supports the idea that breaking the seals might aid the Shadow is that RJ said that the original sealing would have tainted both sides of the OP if women had been involved - but in ToM, Rand voices this concern and it's clear he plans to try something different.

If the note was a plant, why on earth would the Shadow write the second part ("don't bring girl, too pretty"? You're making some huge assumptions. Just because there's no way to definitively prove it's not a plant doesn't mean that theory is worthy of consideration. Furthermore, this has no bearing on Egwene, because she simply doesn't know where Rand is getting his info from - she doesn't even take the time to ASK him why it's necessary. She's become a control freak of the highest order, just like Tuon, Dark Rand, and the Dark One himself. Given her experiences in the series I can see why she's become this way, but I don't like her for it, nor do I think that I'm meant to.