"She was doing absolutely, incredibly well," Lawrence tells PEOPLE. "This blindsided us, just blindsided us."
In November, McClanahan, 76, underwent bypass surgery only to suffer a stroke a week later. "But Rue's a fighter," Lawrence says. "She was getting better and never lost any of her mental awareness whatsoever. She had a little paralysis in he right hand and her speech was a little impaired, but she was amazing."
Each week, Lawrence would check in with her client, who sounded clearer and stronger as time went by.
"She said, 'I'm getting ready to go back to work,' " Lawrence says. "She was a breast cancer survivor and gave speeches, and I said, 'Well, now you'll give speeches about surviving a stroke!' "
Sadly, on Monday, McClanahan was lunching with a friend when she seemed a little weary. Waving it off as fatigue, the actress went to lie down but soon told an aide that something didn't feel quite right.
Not long after, she lapsed into a coma and passed away in the early hours of Thursday, June 3.
"She was a very, very gracious, warm, compassionate lady, and she died with the dignity that she lived," Lawrence says. "Anything else wouldn't have been fair for her. Not for somebody like her who was so vital and always wanted to give."