This is all I can find out about her (from Wikipedia), "Isham's second wife, whom he married in 1653, was Vere, daughter of Thomas, Lord Leigh of Stoneleigh, by Mary, daughter of Sir Thomas Egerton. Four children by her survived him: Sir Thomas Isham, 3rd baronet; Sir Justinian Isham, 4th baronet (d. 1730); Mary (d. 1679), who married Sir Marmaduke Dayrell of Castle Camps, Cambridgeshire; and Vere, an erudite young mathematician who died in 1674, aged 19."
Her article in thepeerage has no marriage date, but her husband's article states she married in 1689 - the dress in this portrait is appropriate for 1653 and not 1689.
Vere Isham wears a hurluberlu coiffure of sorts, with a large horizontal curl from which smaller sausage curls descend vertically. Her slashed sleeves and bodice date this towards the 1650s.
Keywords: Loggan, Leigh of Stoneleigh family, Isham family, British, hurluberlu coiffure, jeweled headdress, off shoulder scoop neckline, chemise, modesty piece, puffed under-sleeves, split bodice, elbow length puffed sleeves, slashed sleeves, necklace, earrings, jeweled bodice ornament, clasps