Despite most of the information we know about Gabby comes from word-of-mouth of the other characters of the show, she has had some appearances in the series.
Gabby is a receptionist at a clinic, and she happens to be the on-and-off hot-and-cold girlfriend of Alice Pieszecki during the first episodes of season 1. Alice decides to break up with her after discovering Gabby had been seeing other women at the same time she was dating her. Gabby shows up again in season two, when Alice discovers she is in a relationship with Lara Perkins, Dana's ex-girlfriend. During her radio show, Alice refers to Gabby as Lesbian X, because of the enormous amount of hookups she has accumulated on The Chart.