"The loss is horrendous," Ann McGregor, 63, told ABC News. "Until three days ago I couldn't look at a picture of Cory, so there's been progress."
McGregor also said that she keeps in touch with Lea Michele, Monteith's former girlfriend and "Glee" co-star, via text.
On July 13, members of the "Glee" cast remembered Monteith via Twitter. Click here to view the cast's tweets and Instagram photos.
"We hold you in our hearts today, and every day we remember your smile," tweeted Michele. "We will love you and miss you always."
Watch the ABC interview with Monteith's mother below: