While making her first public appearance in three and a half years, Céline Dion did something unexpected: She sang.

Last week the "My Heart Will Go On" singer, 55, looked "so happy" when she stepped out for a hockey game between the Vegas Golden Knights and the Montreal Canadiens, Chantal Machabée, vice president of hockey communications for the Canadiens, tells PEOPLE.

"She's been through a lot, and to see her like this and smiling and being so happy...it's amazing," Machabée says of Dion, who revealed her debilitating stiff-person syndrome diagnosis last year. "I know she has good days and not so good days, but this was a very good day, and it was reassuring."

Vegas Golden Knights/X

Céline Dion with son Réne-Charles (second from left) at a Montreal Canadiens hockey game

During the outing, the music legend was talking, laughing and even sang "a few notes," Machabée adds: "It was an incredible moment. She's an amazing woman."

On Oct. 30, Dion stepped into the locker room at the T-Mobile Arena in Las Vegas to greet her hometown team. She was spotted shaking hands with team members and posing for pictures with her sons, René-Charles, 22, and twins, Eddy and Nelson, 13.

After Dion had her visit with the team, Machabeée shared photos alongside the "I'm Alive" performer to Instagram with the singer's arm around her.

"We had a beautiful visit at the game in Vegas yesterday. Thanks @celinedion for your generosity. The whole team is so happy to have met you and your family," she wrote in French alongside the images.

Pascal Le Segretain/Getty

Céline Dion

Dion revealed late last year she was diagnosed with stiff-person syndrome, which is a rare and incurable neurological disease that can cause debilitating muscle spasms and affects the central nervous system, specifically the brain and spinal cord, according to the Stiff Person Syndrome Foundation.

"Patients can be disabled, wheelchair-bound or bed-ridden, unable to work and care for themselves," per the foundation, and the neurological disease with autoimmune features can include symptoms like "hyper-rigidity, debilitating pain, chronic anxiety," and muscle spasms "so violent they can dislocate joints and even break bones."

In May, an insider told PEOPLE that Dion was "doing everything she can" to be healthy enough to perform live again after canceling her concert dates through April 2024.

“It’s heartbreaking that she has had to cancel touring but she is suffering mobility and other issues from the disease disrupting her daily life," the source said.

“She is doing everything she can while working with doctors because she wants to perform,” they added. “She has not given up at all. She is hoping to get all of the issues with this disease under control so she can sing again."