Aran'gar is so convinced that she's so superior to the modern people that she wouldn't see that she drew a line straight to herself by killing them. Beonine gives us a clue too...

KoD
The Dark Ones Touch

“The man who stabs from greed,” she said once the novices were beyond hearing, “the woman who poisons from jealousy, they are one thing. This is quite another altogether. There are two killings, surely by the same man, but well over a week apart. That implies both the patience and the planning. The motive is unclear, yet it seems very unlikely that he chose his victims by chance. Knowing no more of him than the fact that he can channel, you must begin by looking at what ties the victims together. In this case, Anaiya and Kairen, they were both Blue Ajah. So I ask myself, what connection has the Blue Ajah with a man who can channel? The answer comes back, Moiraine Damodred and Rand al’Thor. And Kairen, she also had contact with him, yes?”

...

“No,” Beonin said coolly. “I am saying you must follow the connection. Which leads to the Asha’man. Men who can channel. Men who can channel, who know how to Travel. Men who have some reason to fear Aes Sedai, perhaps particular Aes Sedai more than others. A connection is not the proof,” she admitted reluctantly, “but it is suggestive, yes?”
“Why would an Asha’man come here twice and each time kill one sister? That sounds as though the killer wanted those two and no others.” Ashmanaille shook her head. “How could he know when Anaiya and Kairen would be alone? You cannot think he is lurking about disguised as a workman. From all I hear, these Asha’man are far too arrogant for that. To me, it seems more likely we have an actual workman who can channel and bears a grudge of some sort.”

the only thing that Aran'gar would know for certain that connects Anaiya and Kairen is Cabriana ... she has no clue that Anaiya or Kairen had any contact with Rand.