I don't think that's a military uniform at all. Judging by the rough age of the picture, that actually looks very similar to late 19th- or early 20th-century railway and tram/bus company uniforms. If you look closely on the collar it says C&EI, which might mean this is from the Chicago & Eastern Illinois Railway Company, if your aunt is local to that area.

This is a picture of a C&EI conductor in about 1910 wearing a very similar kepi, so perhaps that's an earlier iteration of the uniform you have there.

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