Something looks oddly incongruous... cowgirl outfit, Buffalo, swastika?

Finnish roundel, more accurately. And the Buffalo was an American aircraft, so it makes sense to me.

OK, maybe it's just the girl who looks out of place then. IMHO.

I must assume that the aircraft was purchased or leased from American parties, then Finland aligned with Germany and thus painted all aircraft in their service?

No...the Finnish roundel has always been a swastika (inverse from the one the Nazis used). The swastika has been a symbol for far longer than Nazis ever existed, it was just them who dragged it through the mud.
This image is supposed to be depicting an American cowgirl who's gone to aid the Finnish and has dressed in their flag AFAIK. Having flown simulated Brewster Buffalos, I can see why; they're fiesty bastards if their opponent is dumb enough to slow down and dogfight.

Artist said he modeled this image after this cover page.

"SCALE AVIATION" 2011/5 published by Dai Nippon Kaiga Co., Ltd.

• http://www.amazon.co.jp/gp/product/images/B004SOXW9A/ref=dp_image_text_z_0?ie=UTF8&n=465392&s=books
• http://www.kaiga.co.jp/emp-bin/pro1.cgi/www/mag/search_results2.html?729

I can see the resemblance, though she looks much more American to me in the drawing, so I thought it was playing on the "American girl in Finnish clothing" sort of deal...but the model in the picture looks Asian from what I can see. Hmm...

OOZ662 said:
she looks much more American to me in the drawing, so I thought it was playing on the "American girl in Finnish clothing"

She looks like an american??? To me she looks like a japanese anime character. Besides america never helped finland in WW2.

I'm personally not seeing the 'cowgirl' stuff that is being talked about. The hat looks more like a puffy beret than a cowboy hat, and there seems to be this assumption that brown boots automatically imply American Old West.