I consulted with ChatGPT (AI). Recommendation:
If your goal is clarity about staging and physical layout,
👉 “The Window Across the Landing” is excellent.
If your goal is simplicity and broader idiomatic appeal,
👉 “The Opposite Window” remains the safest.

"The Window Opposite" ??
With "across" I think I'd like "The Window Across the Landing".
Wendy might a different idea.

How about: 'The Window Across' or 'The Opposite Window'?

"across the way" seems strange if they live on the same landing as we have discovered in the previous part.