She's only been in one or two exposition scenes with him from what I can tell, and most of those were ones where he was teaching her how to be a better whore, which is hardly important or significant for the show (aside from the need to flash breasts at the viewers at regular intervals so they don't fall asleep). So most of her scenes were really more like life-of-a-whore exposition scenes rather than insights into Littlefinger. And if she has been in other scenes with him, then I didn't recognize her... Which seems like already a strong argument against her existence, since it means that viewers don't distinguish between the show's whores and don't care about her character build up.

It just doesn't seem necessary to have her character added to the storyline to give Littlefinger exposition when the show has proven it is fully capable of developing Littlefinger against the real and established characters. Ned in season 1, the scene with Cersei recently where she threatened him, his scenes with Varys, etc.