This is "A Woman with Prayer Beads" by Netherlandish. You'll notice that she's set against a green backdrop, and her silhouette casts a dark shadow onto it. Her chemise seems to be embroidered in black and gold at the neck and cuffs, which gives it a nice touch of elegance. The golden beads hanging from her girdle are probably a rosary, used for prayer. The format and execution of this painting suggest that it was painted in Antwerp or elsewhere in the south of the Netherlands.
The artist has done an excellent job with the details - you can see the golden necklace she's wearing, as well as gold rings set with stones. Her chemise is embroidered at the neck and cuffs, which adds to her refined appearance. The turned-back sleeves and girdle tied around her waist were fashionable in the 1540s.
The painting is an oil on wood work from that time period, and it's likely that it was created using a technique called chalk ground, where several layers of paint are applied. Despite the uncertainty surrounding its attribution, it's clear that this portrait was done with care and attention to detail.
A Woman with Prayer Beads hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.