updated 03/23/2010 AT 3:00 PM ET
•originally published 03/23/2010 AT 4:10 PM ET
While her husband was allegedly engaged in an affair back home in California, Sandra Bullock was happy and completely focused on work while filming her Oscar-winning role in The Blind Side in Atlanta last year, according to sources on and off the set.
“Sandy was the picture-perfect professional while filming The Blind Side,” Bullock’s costar Quinton Aaron, who played football player Michael Oher, tells PEOPLE exclusively. “I learned so much from working with her. I don’t think she was aware of any alleged marital problems and always spoke highly of her relationship with Jesse. My heart goes out to her in this trying time, and I know she will overcome.”
Others who worked on the set also said she seemed friendly and positive. “She was really focused on the part,” says one source. “It was a hard part, and it took all of her attention. She was always very sweet to everyone. But that is Sandra: always kind, always professional.”
Adds another source: “She was upbeat and working, and I didn’t notice anything that was odd.”
Proprietors of local eateries and retail shops in the Atlanta area, where the movie was filmed, echoed those sentiments.