pruning mum

Hi all, i have a mother plant that because i have been building a bigger grow room (those damn ak's) has been in the greenhouse and has got a bit out of hand and has now grow about twice the size i want her to be and i was wondering how much i could prune her back safely ?
Also would she be ok kept in her new box with a propogation light on her ?
cheers Bifter

Take some clones that should help with some trimming

Iwas planning on doing that but she would still be too big