Oh, my bad. I thought just killing the worms would end up with her dead too. What did it need to remove all the worms again? I think it was surgery by Kirei?
Gaim has 2 possible methods at his disposal to kill all the worms inside Sakura. The first is letting Sakura breathe Helheim spores which have unbelievable growth capabilities, taking root even in living flesh to bloom. They can go from spore to flower in less than a few minutes. Despite being in full control of anything residing in Helheim, Gaim can probably guide the spores directly to the worms, grow on them then consume them fully before breaking down into base components. However because of the Grail limiting Gaim's abilities, he can't do this safely. The second method is to feed Sakura Helheim fruit which will force an evolutionary response in her body, basically mutating her, but Gaim can likely still help her control the changes so she won't become something monstrous. And the second path is the safer one
Best case scenario, Gaim can somehow override the restrictions of the grail and regain his fullpowers. By that point he can probably just will the worms to die and completely restore Sakura's body down to pre-modification.