I wouldn't mind another female character; however, I personally believe that Nintendo should first treat the characters they already made with better care. Mario, Bowser, Yoshi, and even Luigi seem to be treated quite well these days; however, the rest of the characters still deserve to be better expressed first before the addition of any more new characters.
Toadette, Daisy, Rosalina, and even Peach herself need to be developed better as well (though Peach has a better status than the other female characters by a long shot). So far, their roles appear to be minor. Even bringing back Captain Syrup or Pauline would be a good move in my opinion.