Hand-my-downs were not uncommon during the time setting of VDT so it's highly likely that it is.

That's what I figured. I like it, either way.

It's not the hide and seek one - that had a pattern in white.

How about the one she wears into Narnia? It seems to be grey.

And here's Lucy in the England sequence in VDT:
http://costumes.narniaweb.com/dawn-treader/england/8-edmund-lucy-eustace.JPG - sorry too big to copy.

No, it couldn't be the one she wears when they go into Narnia. That one is a long-sleeved button-up white blouse, as revealed when Susan takes her cardigan off in Aslan's camp.

Lucy's blouse does look like the hide-and-seek one which Susan wears in LWW, but it almost looks like the train station blouse-- the one Susan wore at the Professor's house when she and Peter were comforting Lucy, right before the hide-and-seek scene.

Oops, I thought you were talking about the cardigan. The dark blue one Lucy wears is exactly the same basic v neck design as Susan's grey one.
The blouses are likely to be common designs of the day.

well, Lucy's VoDT outfit is very similar to this one in LWW:
http://homeofthenutty.com/movies/screen ... be0210.jpg
and here's a shot of Susan's shirt in the same scene:
http://homeofthenutty.com/movies/screen ... be0214.jpg
very close, but not the same.....