Hi Bridget
Unfortunately henna contains metalic salts which react very badly to bleach and therefore causes breakage and severe damage when the hair is stripped of this product. You can give stripping a try but this you will have to do at your own risk as the chances of damage is way too great. You can however treat and strengthen your hair in the mean while and give your hair a chance to grow out before you go that route. You will have to grow out a lot of it as henna is a permanent product and does not shift out of the hair easily.