Yup thats a typical Nitrogen Defiancy and it happens to alot of growers in the first few weeks of flower for some reason they hear that flowering plants dont need nitrogen or alot seem to think they dont need alot when in flower. This is false Nitrogen is a mobile nutrient within the plant meaning like P and K its in constant use by the plant and needed in every stage other than flushing of course and some will even argue that. Just up her grow feed and she should shed the leaves that are already yellow as she has already consumed them and most prob pump out one new fresh set before she starts concentrating solely on buds :) Though best of luck my friend doing a great job so far :) π