The 46-year-old first shared the news of her diagnosis in October (18), and has since become an advocate for those battling the illness, even designing an accessories line expressly for those grappling with symptoms.
Blair's uplifting presence impacted her cast members in the dramatic thriller, who enjoyed their time on set with the "Cruel Intentions" star.
"She's wonderful. She's a bucket full of sunshine and olives and everything good and nice," Josephine Langford tells Entertainment Tonight. "She's hilarious and she's lovely and she's great as an actor."
Langford's onscreen love interest, Hero Fiennes Tiffin, had similar words of praise.
"She's so cool. We had, like, a hour or two conversation outside," he says. "When you see actors who are so funny and confident and just great people and when they say action they're straight into the role and straight out of it and it's just inspiring really (sic)."
The director of the production, Jenny Gage, revealed she had been a Blair fan for years and found their collaboration inspiring.
"She's an incredible actress," Gage said. "I've loved her since I was a 20-year-old girl myself. She's so professional, so passionate and now we see her on this journey. She's such a strong, incredible woman and such a force that it's been great having her on the movie and knowing her afterwards."
Blair is set to be recognised at the 26th annual Race to Erase MS gala in Beverly Hills, California next month (May 2019).