Actually, the best counter against Jackie is 5-pilling something that can reasonably stand up to her (Ghumbo, Selma, GraksmxxT, etc.). Most Jackie players tend to play 3-4 pills since they don't expect you to stand up to her. It's only good against decent players, though. Good players can see right through that
Dorian 3*, Tyd, Glosh, Vinnie, Lyse Teria Cr, Azgroth, Tanaereva, Hikiyousan, Greow, Zatman, Janice, Eyrton are some examples of cards that can face her on equal footing.
(Notice how short my list is... if it were any other card I could think of at least 30, including the Big Five aside from Lyse Teria Cr. Jackie and Zatman were so broken that they ruined Uppers, IMO.)