chasv77answered grow question 4 years ago If you don't know the estimated stretch for your strain, count on doubling in size, if growing conditions are good in veg.
Find the manufacturer's plant distance from light source, and that is what your flower should wind up with, in a perfect world.
If she starts vertical stretch faster in flower, you will have to do LST early, before buds start to ripen, to stay within recommended distance from light.
FYI, I can get within 6" of my 180W LED light, before leaf burn.
Formula (Current height x 2) + rec dist = total distance from light to top of soil.