GR translation: the translucent guardian of a rainfall

[Mike Jing]

V94.8-15 ,P96.1-9   The cameraman is pleased at the unexpected effect of so
much flowing crepe, particularly when Katje passes before a window and the
rainlight coming through changes it for a few brief unshutterings to murky
glass, charcoal-saturated, antique and weather-worn, frock, face, hair,
hands, slender calves all gone to glass and glazing, for the celluloid
instant poised—the translucent guardian of a rainfall shaken through all
day by rocket blasts near and far, downward, dark and ruinous behind her
the ground which, for the frames’ passage, defines her.

Several things:

In "changes it for a few brief unshutterings to murky glass," what does
"it" refer to? I always thought it refers to the crepe, but the published
translation took it as the window, which seems redundant to me since it's
already made of glass.

What does "the translucent guardian" refer to here? I thought it refers to
the preceding image of Katje in the dress, while the published translation
again interpreted it as the window, which doesn't seem right.

What does the word "downward" describe here?

In "dark and ruinous behind her the ground", does the "ground" mean
"background"?