You could put her into flowing right now if you wanted to, keep in mind she will stretch up to three times the height it is during flowering. This looks like an indica dominant strain which are typically less prone to drastic height changes during flower but that's all genetics so who knows. If your not in a rush you could read about pruning techniques like topping, LST, etc to improve your yield.
As for the re-potting there's lots to read about when to repot and how but when it comes down to it really you just know its time to repot. I tend to notice the watering schedule becomes much sooner than it used to be. I like to water small amount more frequently and one day I realize wow I'm watering this damn thing every day. If I ignore that growth rates slow down shortly after then its a rush its definitely time to repot.
Because you just switched to "better fertizering and watering" Id recommend doing nothing for a week or so to see how she responds. Then repot maybe then switch to 12/12 if you desire. baby steps not all at once keeps things stress free and healthy.