Her article in thepeerage is here. She bore 12 children.
From Pinterest search reduced veiling reflection in upper left with Photoshop. Also posted to the Transition from Ruffs to Collars - 1620 to 1630 Album here.
Coiffures are not going to change for decades to come. Her bodice is framed by expanses of white from her collar and sleeves.
Keywords: 1629, Mytens, Catherine Howard, Catherine Cecil, Countess of Salisbury, Howard family, Cecil family, Countess, British, straight coiffure, jeweled bun, earrings, necklace, chemise, trapezoidal décolletage, lace collar, bows, puffed virago sleeves, arm bands, laced bodice, waist band, natural waistline