According to Max von Boehn this is Sibyl of Cleves in bridal attire, by Lucas Cranach 1526 Wiemar Museum.

I cannot recall where this image resides on the internet. If anyone knows, please tell me and I will link to that page.
She wears a wide necked, closed front dress in velvet. The ubiquitous gold broade banding appears at her waist also.
Under her gown she has a high necked partlet or chemise, which terminates in a 'dog collar'. These collars also appear on women with out a high neck, so it seems that they are separate items. Or at least can be seperated.
She has a wide necklace with a medalian that rests on her partlet/chemise.
Over her gown she wears an extremely long, very wide gold chain, wrapped several times around to fit the neckline of her gown. The neatness of the chain is either artistic licence, or perhaps stiched in place for such an occasion.
Note her hair is unbound, which strengthens the title Boehn has given.