Dunno if thats real flower or preflower/ sex showing. In flower u should threat her like a princess while u can torture her in vegatetive phase.
Also its not light burn on the bottom leafs, thats just unlogical when the light is coming from top. Its probably a N shortage or too less or too much water, probably too less if i look at the plant.
In a plant like this i wouldnt defoliate at all, she can use the chlorofyl to produce buds. Its another story when u have ur whole growroom full with plants.
In general; if u want a bushy, short plant u should top her and if u want a tall open plant you shouldnt top her. I know u probably meant the leafs when talking about bushy but still, a topped plant will produce more leafs also.