"I would like to thank all of Cory's supporters at this extremely emotional time," she Tweeted. "Your support has been overwhelming … thank you!"
The 31-year-old actor was found dead in a Vancouver hotel room on July 13, from a lethal combination of heroin and alcohol.
Since then a number of people have come forward and spoken to the media claiming to be family insiders.
McGregor addressed that issue on Twitter as well, saying, "The person releasing articles relating to my feelings and thoughts on how to take care of Cory's ashes has never been in contact with me." She followed it up with, "I have never met or spoken to this person. He does not represent me or my wishes."
Fans of Monteith may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver's Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.