while she was in a mad rage ... she was so careless she got physically leaped on and basically killed for lack of being aware of anything but Rand.

I find it a huge leap to assume she took the time to put wards in place since the scene essentially starts with her blowing a wagon up, skinning a darkfriend and then going on a mass murdering spree to get her insane hands on Rand ... she clearly wasn't thinking clearly!

Of course I recognize that my idea is not without it's holes, but it seems reasonable that Lanfear, who knew LTT for hundreds of years would be able to pick up on even a small gesture ... it's like they say in gambling ... everyone has a "tell" ... any visual clue Rand gave that he was beginning a weaving would have been clue enough that she needed to slice a flow and the most likely place for her to slice would be around his body, most if not all weaves generate from around a Channelers physical body so again not hard to figure out where to aim the weave slicer.

As to Verin, it's clear that she picked up on Graendal's Channeling, but we know from a variety of quotes in the series that inverted/reversed weaves cannot be seen or felt by anyone except the person weaving them. Perhaps Graendal threw a Fireball at them or something else that had a more visible effect ... any number of explanations as to why Verin would have been able to tell that she was being Channeled at.