Basically shes being fed tooo much , I would suggest just using ph'd RO water for abit till your leaves stop burning . Your suffering from a lock out in micro nutrients and that's why your leaves are yellowing like that , if your plant only has 3 weeks left and it's still burning after you flushed her just feed with ph'd water and she will have enough nutrients in her to finish the cycle and flush properly . I hope this information helps you on your quest to the finish line . Happy Growing!