She’s lacking something guys but what?

So as an experiment I decided to let my girl veg a lot longer than I normally would have. She is now in week 4/5 flower feeding has never been a problem. apart from the fact she will not stop growing no matter what I try to the point I now have a 5ft wide monster on my hands! All of a sudden she has flopped slightly and gathering yellow with brown spotted leaves! Pics are as follows 1st is the top of canopy! Yes this is one plant
2nd is the suspected problem any advice welcome thanks guys x

Mild looking Calcium+Mg deficiency.
Other than that plant looking good and buds are getting chunky as should.