The only thing Yumeji can do is give Merry the confidence that it's alright to 'send them back'. Or act as a human shield.
I'm not yet convinced we have seen all of Yumiji's powers or that Merry can't do fancier tricks again, like she did after Yumeji had been wounded. Not all shows need to be tainted by shounen power-ups, of course, but we simply still know very little.