Board Thread:Questions and Answers/@comment-46467817-20200728061502/@comment-2182964-20200804081024

Aside from those Hollow holes that are visible in the series, most of the Hollow hole locations were revealed in databooks.

Her Espada tattoo covers much of her back, and all but the top of that tattoo is visible, so we can at least say it isn't in the general area of her tattoo. Brave Souls, meanwhile, opts to install the Hōgyoku in her weapon, rather than reveal the location of her Hollow hole in the special illustration they released. The only other case of this occurring that I remember was Szayelaporro. The Hōgyoku is inserted into his tail.

So, in summary, we don't know.