On October 11, 2018, Niantic announced a surprise event lasting 24 hours! October 11th is “International Day of the Girl Child” and as a result, the following Pokemon are more frequently spawning in their female form:
Shiny Nidoran♀
Twitter Announcement
Trainers, a greater number of female Pokémon have now been spotted in the wild until October 12 at 1 p.m. PDT. Keep an eye out, as lucky Trainers might also spot a Shiny Nidoran♀, Nidorina, or Nidoqueen 👑 ! Enjoy searching for Nidoran♀ and friends on this special day! pic.twitter.com/LJdTKdNNj8
— Pokémon GO (@PokemonGoApp) October 11, 2018