That's a really good point! Initially, I thought it would be best to wait until the MC is more open about exploring that part of her sexuality before introducing the girl-on-girl relationship arc. However, you make a strong case for including it at the end of v0.4. Thanks for pointing out the oversight, it's helpful for future development!
It's your game, you don't have to introduce girl-on-girl relationship arc faster than you feel is right for your story.
But, if it just because you want that introducing lesbian relationship seem plausible (and not just to check another kink in tag list), I think there are believable way to do it.
Even if Ami isn't so open about exploring lesbianism for now, depending of the player choices, she could already have fantasized about Jessica.
So it would not be a non-sens that she watch some lesbian porn.
She could begin to asking herself about her own sexuality, like "Am I gay? I'm curious, would lesbian pornography really turn me on?"
Or even some sort of denial "I'm not gay! I'm sure watching some lesbian porn won't arouse me. See...".
But as I wrote, it's your game.
You should do as you feel is right according to your vision, of what you want to tell.
Not just to please some random dude who perv on girl-on-girl lewd actions
