Jasper will not -- which means that Malachite is trapped there by the Lady's will, unable to even physically struggle against the awful force keeping her face down in the water.

It takes longer for her to drown. Her torsos heave against the inevitability of it, to no avail. When it starts to be absolutely unbearable Jasper finally relents her frantic grip on the fusion, but it's too late, by then. Her four eyes dart around in increasingly sluggish panic, until at last they flutter closed and her massive, monstrous body goes as limp as the Lady of the Lake's grip will permit.