Rosie O'Donnell (search) is an actress -- but she was a talk-show host for so long and such a controversial figure after that that some viewers may have forgotten this fact.

But they will remember on Sunday night (9 p.m. EDT) when they see her in "Riding the Bus With My Sister," (search) in which she plays Beth, a mentally handicapped woman whose sister joins her in her favorite pastime: riding the city bus.

O'Donnell told FOX News' Bill McCuddy that playing Beth in the Hallmark Hall of Fame drama was "a very scary thing to do."

"When she was young girl (she is my age, 43) they called her retarded, but she now falls somewhere along the spectrum of autism, which is a wide and varied spectrum ... she has minimum social skills or interest in anyone outside of her own world.

"She is a fascinating character to play and it was a very scary thing to do. But with Angelica Huston (search) directing and Andie [MacDowell] helping me get through it, it was a magnificent journey to try to do it," O'Donnell said.

Sometimes, O'Donnell's celebrity interfered with shooting.

"We shot for about six weeks up in Hamilton, Ontario, and they had this great huge bus that had cameras and lights on each side. It looked like a UFO. Driving around this little town, people would come outside and they would see me and scream, 'Hey Rosie,' and we were like 'Cut!'"

And she does miss her talk show sometimes.

"I thought the maximum would be four years and I did six ... So, I look back on it fondly and I do miss it. And I sort of miss having the platform so I started my on blog, which is better than a show because nobody can answer back," she told McCuddy.

Huston, who steps into the director's chair for the third time for "Riding the Bus," says she jumped at the chance to collaborate with O'Donnell, who also served as executive producer.

"She was a total pleasure to work with, extremely talented. She comes very prepared and is good to everyone," Huston told the Associated Press, calling her star "a major goodwill ambassador."

Inspired by Rachel Simon's autobiographical book of the same name, the film chronicles the relationship between the assertive but dependent Beth and smart, self-absorbed Rachel (Andie MacDowell (search)).

Their uneasy sisterhood changes when Rachel joins in Beth's daily pastime of hanging out on city buses — her way of interacting with a world that's sometimes harsh, sometimes kind.

The film eschews sentimentality in its depiction of Beth.

"You don't want to embrace her at all times," Huston said. "I think the movie comes from a pretty direct point of view — which is this person is at the same time enchanting and exasperating, adorable and irritating."

FOX News' Bill McCuddy and the Associated Press contributed to this report.