There's NO WAY to maintain correct soil chemistry in the small a pot and she WILL die before harvest looking like that.

If you can't do a correct transplant, do a double-pot where you fill a 5 gallon pail with fresh soil to within 4" of the rim, then take a sawz-all and chop the bottom 4" of the current pot off, avoiding the roots- or a pair of tin snips if it's a thin pot- and place it ON the other soil. The fill in the sides.

FLUSH WELL before you do this and allow to dry out again. Your plant is showing signs of soil salting.

You also MUST feed a correct bloom fert.

That plant will probably finish rootbound even in a 5 gal pail. Ideally, a large feed tub or trash can cut down to about 3 feet tall and punched full of holes with a power drill and 3/4" paddle bit would be better.