The Nothing Compares 2 U hitmaker became suspicious when it emerged the Back to Black star had an estimated worth of $9.6 million (£6 million) on her death in 2011 despite selling millions of records worldwide.
Now she has blasted industry bosses and accused them of taking advantage of a bankable star by forcing Winehouse to tour even though she was falling apart.
In a post on Facebook.com, O'Connor writes, "As an aside, does anyone else think its odd that Amy Winehouse was only worth 6 million quid when she died? Do the maths. Have a look at the points in her publishing and recording contracts. How many records did she sell? How many tours was she marched out to do out (sic) despite being clearly unwell? If you did it to an animal you'd be locked up."
Winehouse passed away from alcohol poisoning at the age of 27 in July, 2011.