Semirhage doesn't torture the Aes Sedai to get information about the bond at all. Semirhage's curiosity about the bond during the interrogation is merely her own. She likes 'experiments' about stuff she doesn't understand much like Nazi doctors as Mengele did. She just let herself be distracted by that.

She wasn't even supposed to get a warder - the Myrddraal were asked to capture an Aes Sedai and, as Semirhage comments, Myddraal always associate warder and Aes Sedai for some reason she doesn't understand, and brought her both.

Semirhage (who had no idea what the information would be used for) was asked to torture this captured Aes Sedai, who was Cabriana Mecandes (a blue sister, close friend of Anayia and Kairen) to get from her all the necessary information to build up a legend for Aran'gar, who was sent to infiltrate Salidar. Aran'gar got from Shaidar Haran all Semirhage managed to get out of Cabriana and it was used to build up the legend of Halima, an invented travel friend of Cabriana before Cabrina supposedly had an accident and died, and who told her friend about Salidar.

That's what it was about, not the bond.