I figured this out from the pixiv tags by the artist: this isn't maria_(umineko) but ushiromiya_maria (artist has 右代宮真里亞 as his tag only and not マリア卿 for her alter ego).
She's dressed in the uniform of the eiserne_jungfrau (artist has the tag アイゼルネ・ユングフラウ) So I added the eiserne_jungfrau and eiserne_jungfrau_(cosplay) tags.