No problem, I think. First we do the hero's introduction, then we do the heroine's -- and I even got it all outlined on that principle.
Then I sat down to write it.
And it sprouted some nice, interesting complications, which did a good job filling out the story and giving it local color. Some minor characters appeared to move the hero's story along, and suggest additional plot complications -- which have to happen before he meets the heroine.
And how long do I want the story to go on and on (and on!) before she shows up? It's hard to convince people that someone who's just shown up in Chapter 13 is a major character. And while I could be a little more medias in my res, there's an awful lot of backstory even if I begin where I begin now; there will be heaps more if I start when they meet, much of it directly related to things that happen just after that.
Alternatively, she does have a backstory. I pick up the ten-foot pole and poke at it. And the villainess is perfectly willing to show that she's crazy and hates the heroine much earlier -- I think. I shall have to try to write it, and see what happens, given what happened when I wrote the hero's.