Abby may have only been in a few episodes of How I Met Your Mother but she played an important role in the relationship evolution of two main characters. Princess of Pop Britney Spears’ turn as the slightly unhinged Abby on How I Met Your Mother was one of the show’s more memorable guest appearances, and was the singer’s first acting gig since a cameo on Will & Grace a couple of years earlier.

Abby was introduced during the third season of How I Met Your Mother in the episode “Ten Sessions,” as the receptionist at the dermatology clinic owned by Ted Mosby’s future runaway bride Stella Zinman. Over the course of the ten sessions it took Stella to remove Ted’s butterfly tattoo, Abby developed a massive crush on Ted. Unfortunately, Abby’s romantic overtures went over Ted’s head due to his own crush on Stella, and after meeting Barney Stinson she became yet another notch on Barney’s crowded bedpost.

Naturally, Barney did his usual thing and slept with Abby and then ghosted her - which led her to seek hilarious payback. In the season 3 episode “The Bracket,” a mystery blonde woman was sabotaging Barney’s attempts at picking up women by stalking him and informing his potential conquests of his womanizing ways. Although the mystery woman in “The Bracket” – handily only seen from behind – was actually played by Tess Parker (True Blood) rather than Britney Spears, it was revealed in the penultimate season 3 episode “Everything Must Go” that Abby was Barney’s saboteur.

That was neither here nor there, however. Rather, it was what happened during Barney’s mission to discover the identity of the mystery woman in “The Bracket” that made Abby so important. In this How I Met Your Mother episode, Robin Scherbatsky helps Barney by pretending to be someone he’s hitting on in an attempt to snare the mystery woman and find out who she is. While Barney and Robin are pretending to flirt with each other she asks him what he says to women to get them to sleep with him. Barney whispers those magic words in Robin’s ear and notes she’s a little turned on by it which seems to be the case despite Robin’s protests.

Not so coincidentally, Barney and Robin slept with each other for the first time a couple of episodes later. Considering the role Abby played in Barney and Robin’s supposedly faux flirtation in “The Bracket,” it’s arguable she was the impetus behind them getting together. Although it took Barney and Robin a while to make it official, in a roundabout way Abby brought them together and thus gave How I Met Your Mother one of its best couples.

Next: How I Met Your Mother: What Happened To Jennifer Morrison’s Zoey