I've done some photo grows, finishing a 20+ week sativa right now, so hopefully some of this helps...
1) Leave her on 12/12 until you chop...from here, I'd only ever DECREASE the daylight period, for example on my longer strains I go to 10/14 in the last 20% of the flowering cycle to encourage ripening and maturation of the buds.
2) She will eat more nutrients and grow more roots since she'll be alive longer than an auto. Keep in mind that this is still a strain with auto genetics in it, so it's not going to be 70 days of flowering. I'd generally guess that you'll be looking to chop her down about 45-55 days from the day you transitioned to 12/12. Remember that day, count forward, use that as a rough guess. With this strain, I believe your goal will be to harvest when the plant starts to fade and trichomes mature to an amber/milky split, so you should consider a soil-cleanse around 7-10 days prior to your anticipated harvest date. This will allow you to plan when you cut the nutrients, so essentially looking to cleanse on day 40 and see where she ends up.
3) If you don't have a 30x microscope or jeweler's loupe, go buy one...they're single-digit price range for an effective cheap one. You want to get good at analyzing trichome ripeness with a magnifying device.
4) Don't be afraid to feed. I grow organically (don't check my PPM) and in coco coir (hydoponic medium, VERY effective). When I'm in coco I feed daily at about 600ppm. If you're in soil (didn't read your whole thread) then you should feed her with about 600ppm of feed every week, maybe twice a week. Someone with more conventional experience can chime in, but basically she has big roots and is much more mature at the onset of flowering than her autoflowering sisters would be. This means she can now handle "regular" fertilizing whereas an autoflower needs more delicate feeds early on because her roots are developing simultaneous to bud development.