As I noted above, Margot Honnecker was not a full or even candidate member of the Politburo. Even in 1987, "the only two women members, Ingeborg Lange and Margaret Müller, candidates for thirteen and twenty-three years, respectively, were not selected to full membership." http://www.country-data.com/cgi-bin/query/r-5120.html
There's also the small problem that as far as I can tell, the rest of the Politburo hated her guts. By the 1970s, the ruling heads of Warsaw Pact states are generally of the "someone everyone can live with" persuasion.
As far as Elena Ceausescu, she was so loathed in Romania that there's a 50/50 chance of a mass uprising if she ascends to power, an uprising that the Soviet Union would love to be able to get behind.