It's entirely possible she has no such ability. It could just be the artist employing Rule of Funny to exaggerate the effects of turning a sword into a copy of one's body by transferring one's soul into it.
I believe it may be a reference to the theory of her body being her real sword and her sword being her real body, the method of immortality achieved by a Shikaisen. I recall someone mentioning it before.
http://en.touhouwiki.net/wiki/Shikaisen said: it is required that a person "fake" their own death by substituting a bewitched object like a bamboo pole, sword, talisman or a shoe for their corpse
I don't know why but I'm just imagining the narrator from Jojo explaining this just as he did with the abilities of the Pillar Men (pretty funny actually).
Tkk Tkk TkkToyosatomimi no Miko, member of the noble clan, is a shikaisen. By causing her soul to inhabit a treasured sword, she is able to alter her own body into a blade!It's my turn to do the cooking today.KchkkI'm sorry.Oops...Spl-littI've told you not to use your own body for daily tasks, haven't I?Hebpshew