So if you Linked with someone, for example, and then Travelled around the world, the Link would have weakened and stopped providing a boost due to the spacial difference. It is the same with maintaining a weave - unless you tie it, or specify a period in which the weave should fade, your weave starts weakening as you increase your distance from the object. This happens all the time - the Bond's emotional connection fades with distance becoming nothing but a vague sense of where your partner is, while Moiraine's weave with the coins became less certain as the distance grows.

So, once again, going with a simple explanation: any number of things could have caused the weaves to fade on Rimshalar. Even more obviously, Graendal could have Travelled away once a warding tucked into the net of Compulsion alerted her, and then as soon as saidin triggered another warding, she could have let the Gateway closed. I mean, we saw a Warding net mixed with Compulsion that made the messenger die if Rand refused some terms - I think there is a lot more possible than we've seen so far.

I just would rather go with a character's modus operandi to base my theories and Graendal's has always been a willingness to abandon everything, even her worshippers, if it meant her survival. And I just don't see her trying to get Rand to come to her - all indications are that she was intimidated by all the failed attempts to defeat him and wouldn't stick around to see what his mindset was (she probably already knew since she has such an extensive spy ring; heck, another good theory is that she made up the whole thing, implanted a suggestion in a librarian's mind and did all of this just to buy herself time to flee with her servants to a new headquarters).