I didn't watch Passions, but I think this is also the classic soap archetype of the "bad girl." Blair Kramer on OLTL, Carly on GH (as played by Sarah Brown at least), hell even Erica Kane, were all popular bad girls. The bad girl is the woman who plots, schemes, lies, and in short does anything to get what she wants--but the audience still loves her because she's also vulnerable and tough. There's always something tragic about the bad girl because often she's doing all this for a guy who doesn't love her enough (or who loves someone else)--or she's doing this because she doesn't believe he will love the real her (or the person she is without lies). And her schemes never work out on the long run--she's usually left to pick herself up out of the ashes alone. The bad girl is, imo, the heart and soul of any good soap opera. Her desires define a soap. Even though she's often the antagonist to a "good" character--she's never a villain because the audience is rooting for her, even if they don't root for her schemes.
I never really thought of Rebecca in these terms because Crazy Ex-Girlfriend has such a different tone than the soaps I've watched--but yeah, you guys are right, the show is kinda like a deep examination into the mind of soap opera bad girl if she happened to be a West Covina lawyer.