A gap year where you so something beyond simply re-taking standardized tests could make a meaningful difference in your applications. But that would require that you do something. Things are ratcheting up for the 2020 elections. If you are serious about Poli Sci, you would already have attached yourself to a political campaign of some sort. Have you done that?
You got waitlisted at a number of excellent institutions. That tells me that your application even as it was last fall, was a pretty strong one. Bryn Mawr, Smith, and Mt Holyoke might have been admits when Wellesley was a waitlist. Agnes Scott, Spellman, and Hollins almost certainly would have been admits.
How much money do you need? Generally speaking, transfer admission is more difficult than freshman admission, and certainly merit-based aid is usually a lot worse for transfer applicants. So yes, if you would need significant aid to attend places that you like better than UNR, one gap year can make lots of sense.