In the mid-1990's, after the Internal Revenue Service dunned her for taxes owed by her long-divorced first husband, Elizabeth R. Cockrell helped lead a successful campaign to change the way the agency dealt with the innocent spouses of tax cheats. Now she has set her sights on changing the way New York courts use forensic evaluators. ''But fighting the I.R.S. was easier,'' she said, because at least she could turn to Congress for help. The evaluators, she said, seem to be accountable to no one.