I'm assuming this is a photoperiod? The plant is looking fairly stressed from something.... you don't provide any information about any extra nutes you may be giving her but she's looking like she's been overloaded with nitrogen. But the other issue is your pH level... you need to bring that down to somewhere between 6.0 and 6.5... in flower, you'll need to be between right around 6.2/6.3... weed needs acidic soil to grow well!
If you ARE giving her other nutes, I'd lay off them and give your girl a good flush adding in 1/2 strength nutes to the final gallon ... if you AREN'T giving extra nutes, I'd just give her only pH'd water for the next week or so and she if she recovers.
Good luck!