AO3 is an archive started by slash fans; I doubt it's representative. If you take other websites such as Fanfiction.net or Wattpad into account, I'm sure there's more het than anything else. But even if stories about women were a minority of the fic out there, that wouldn't make them less worth reading. Going instead to m/m stories and wondering where all the women are seems disingenous. If you want to read more fic with women, seek out the stories that involve women. As havocthecat says, femslash authors would appreciate more comments and kudos.