Despite the friction and the banter, Isla and Sadie are pretty much best friends. Their friendship blossomed out of their working relationship; Isla was assigned to be Sadie's Primary Assistant when Sadie first volunteered at the BrasByDesign Research & Testing Facility almost two years ago. You can read a little more about it in BrasByDesign - Lore, The Universe and (Almost) Everything.
Still, it's hard to ignore Isla's fixated gaze upon Sadie's enormous bosoms. Whilst Sadie has steadily grown, so has Isla's obsession with her subject and friend's development. Occasionally she'll just zone out, staring with fascination at the those two magnificent over-developed tits. Perhaps she deliberately takes her time? Maybe she loves more than just her job?
Does Sadie know? Well, she might be starting to get a little suspicious, but in all honesty, she has far bigger things to think about. Once she's finally fitted, and Isla snaps out of her daydream, she's off to the Testing Department for further 'treatment'...