Agreed, give her a dose of vegging nutes and some epsom salt and you should clear that up. The lower leaves are gonna turn yellow though the longer into flower you get no matter what you're feeding her but that's not for a couple weeks so the veg nutes should be fine for now
Av got same prob but mine is due to Symphilids in the medium little fuckers if u want to check 4 them wen u water ur plants watch the top of the medium an there will be little White things running round.
This is perfectly normal has the plant nears the end of its life it has pulled all the nitrogean from the leaves thus leaveing them yellow.5 week is about the perfect time to see this happening to a plant in flower all though some that i have grown have produced nice weights and kept green till the very end.I would let this strain have a couple more weeks then advised by the seed company has it comes into its own with a extra 2 week you will get more crystals forming....tyke.................