Same things happening to me as well, but other way around. I popped an “auto-flower” seed and after 8 weeks it’s still in veg, definitely a photo period. Really changes the game plan eh!
don’t worry, autoflowers will flower naturally and automatically under the 18-6 light schedule, and doesn’t need any change. You should be able to keep it in the same tent with the same light schedule and have the others Just veg around her.
The nice thing is it’s an auto, so it shouldn’t change your routine much except nutrients being given etc (I wish this was me because I’m looking for a place to make the 12/12 flip with my photoperiod girl instead as my other tent is being used for drying lol)