A very good question and the WikiTree Help Page on this is not clear on this:
The problem lies in what is the Parent High Category for your category. Possibly American Artists or American Painters or both. Both of which Copley is already under as an individual. I looked for an appropriate Parent Category, but was stymied there.
Possibly just an addition to Lucretia's Profile along the line.
Lucretia's portrait was painted in 1769 by noted American Artist [[Copley-487|John Singleton Copley]].
This would then send them to his Profile where life and work is represented and would give the viewer a better sense than just a category.
Also found this on her portrait which gives the date of the portrait as wel for a source. http://npg.si.edu/object/npg_1969.37_WOR
Hope this helps you. To get more help, repost your question with the tag categorization.
Also found this on a John Murray (McMorrah) of Rutland. You have to scroll through it a bit. http://history.rays-place.com/books/htone/rutland.htm