Hey bro, those are some fine-ass ladies!! +rep :clap:
I've had leaves turn yellow on me in the past due to the plants getting too dry between waterings before. I hypothesized that with it being so dry, it was sending all of the water and whatever nutrients it could from its oldest fan leaves to the tops of the plant to try and keep photosynthesis going on since the roots weren't able to draw anything from the soil. Dunno if that's at all correct, but something I thought of while medicated. But it's happened on a couple of grows that got really big and were in small'ish containers. Yellowing occurred just like what is in your pics.
:smokebuds:
Edit: Might it also be due to the fact you said she just had a big growth spurt? Maybe that used up a good deal of N in the process?