sure, just make sure she gets 12 hours of COMPLETE & UNINTERRUPTED DARKNESS on the 12/12 cycle...if you only have one plant though you may want to hold off for a week or so if you can and try to get her closer to 16 or 18"--your yield will improve quite a bit, esp. (& only) with sufficient lighting (I'd recommend, for 1 plant--400HPS) and cutting only the lowest branches--but you didn't ask all of that.....so,yes you can force flower at any time pretty much after roots are good and established...(or at least i know this is true for cuttings/clones)
I see you are brand new to the site--so am I--so HEY! WELCOME US!!
I'll admit, I've been "lurking" on here for a while--couldn't stand not getting to see the pics or communicate..
TONS of useful information and such an intelligent, knowlegable, funny and HELPFUL community on here...
I am interested in adding one of those silly disclaimers to my posts --as, though I participate in no actual criminal activity, the one thing that kept me from registering for so long was both my real and imagined awareness of big brother....(but mostly real)
anyway good luck w your lil girl...is she your first? are you even sure she is a girl???????