Your sister's furniture is absolutely lovely! I'll bet she's thrilled. I'd say the dates you're getting here sound about right, 1920-1930ish. It does have an Art Nouveau flair. Here are two that may interest you: This one is more deco than hers: http://www.french-warehouse.com/FW1365.htm This one is more true art nouveau and is dated much earlier: http://www.burchardgalleries.com/auctions/2004/oct1704/01images/l8.htm

What I think we're seeing in the pic is a fixed pane that runs from the corner (where the walls meet) to someplace beyond the left edge of the pic. Then 2 panes, one of which is seen slanted from the ceiling to the window opening (in this open position), and another that is hidden behind that so the top of it is tucked up to the ceiling and the bottom is hinged to the top of the pane we see. When its closed seems like it would look like a fixed pane at the top and 2 panes below. The small wall from the left edge of the window to the corner seems to serve no purpose and could be just window. Unfortunately I came across the pic on a decorating site, or maybe a countertop site--don't recall as I've had this in my idea file for a while. Guess it could be custom made, but was hope somebody might know more about a source that manufactures them. Like maybe this window is used in some commercial application or something.?.? Pretty cool, though, huh? I'd really like to have this in my kitchen for serving snacks and drinks.

you'll probably have around 24-28 inches wide by 36-39 inches high casement windows milled together ..glass size depends on brand and frame and so forth. the windows shown are only about 21 wide by 28 tall or so....note they aren't even as high as the 30 in wall cabinet door shown. If you want casements to look traditional, get the panes. The taller narrow window you'll have would be nice as a casement.

Could be Viking? Looks like ours from the 80s.