If she is still stretching you can, but I always try to do my topping/FIMming in veg. If she's still fairly flexible you might try a bit of training to increase your yield instead. Normally the tallest/main cola will get the biggest, but if you train the tops so they are horizontal/even with each other, the hormone levels won't favor the main cola anymore and you'll end up with a wider canopy of medium buds instead of one big one. I'm probly doing a terrible job explaining... Do some searches on LST (Low Stress Training), supercropping and ScrOG and I'm sure you'll get the idea.