It was revealed in
New Avengers: The Reunion that the Mockingbird who reconciled with Hawkeye and was subsequently killed was actually the Skrull. Mockingbird's last memory before waking up in a Skrull prison was of the airport on her way to deliver the news to Clint that she'd filed the divorce papers and they were officially no longer married.
And then the Skrulls basically tortured her by creating a false West Coast Avengers HQ and impersonating the WCA just to mindf*** her. She ended up breaking out, getting caught again, and ultimately killing the lead Skrull, who had disguised himself as Hawkeye.
So when she came back to Earth, she was conflicted about her relationship with Clint, to say the least.