Kate survived her husband by about a year, dying sometime between 31 October 1583 and 20 June 1584.
She had been alive to make a contract with John MacCorcadill regarding the teinds of Killin on 31 Oct. 1583 (GD112/51/98/8) but by 20 June 1584 those teinds were being leased to her son, Black Duncan (GD112/51/98/90).
A later lawsuit stating she had died in Sept. 1580 must be incorrect. (25 Jan. 1588, Register of Acts and Decreets, CS7/114 fo. 64).
Unfortunately, Kate's Will and Testament has not survived. Other 16th century Campbell Wills were registered with the Edinburgh Commissary Court (NAS CC8/8).