Lemon Skunk - Plant 2 of Perpetual Grow

I never experienced it myself but it seems that its a common theme these days with certain genetics/breeders. You only really have two options. One, wait it out and like you said it may be a 15 week auto. Maybe she had something that stunted her and it happens (for example if you look at my sweet tooth that's what happened). Option 2, you'll need another area where you can put her on a 12/12 schedule for a week to force her into flower and put her back on whatever light schedule until harvest. Hope this helps.