Nah, he just doesn't like ugly bitches.
Really, he actually is very sexist (as is SW in general) so that probably was part of it. And she was very old. Being powerful isn't enough to make someone a good apprentice (Dooku was just an interim between Maul and Anakin). Kadann was supposed to have been very powerful too, but Sidious passed him up as well (probably because of age).