To hear Sally Field tell the story, she had to put up a real fight to land the role of Mary Lincoln in Steven Spielberg’s Lincoln.

The director first approached her about the part around 2005. But there was no script or leading man. “I read many versions written by many writers, and it was never anything I thought Steven would actually do,” Field says. “It was the grandest idea, and I couldn’t see that it was ever going to be.” That changed when Tony Kushner came on board to write the screenplay and Daniel Day-Lewis replaced Liam Neeson, who dropped out, as the 16th president. Field told Spielberg she still wanted the role.

But her first audition felt wobbly. “I think part of it was age,” says Field, who is 66. “I’m 10 years older than Daniel. And Lincoln was 10 years older than Mary. I’m 20 years older than Mary. That’s a legitimate concern. You have to be worried: can I really pull that off? Steven, rightfully so, said the lighting will be harsh. Daniel is not going to be wearing any prosthetics. And so he had to make sure that Mary fit with him.” Spielberg watched the video of Field as Mary and compared it with the footage of Day-Lewis as Abe, and told Field it wasn’t going to work.

The next day, he called her back. Day-Lewis had seen the audition, and he wanted to fly in from Ireland so the two could read together. The re-imagined presidential couple met one afternoon in Los Angeles. “I drove home, and as I was getting home, my cellphone rang,” Field says. “It was Steven and Daniel together, saying, ‘Would you be our Mary?’” Field’s performance recently won her Best Supporting Actress from the New York Film Critics Circle. She spoke to Ramin Setoodeh about finding Mrs. Lincoln, whether the president’s wife was bipolar, whether he was gay, and why it was such a pain to use the toilet.

Are you here in New York, where it’s rainy and dark?

Yes, I am. I like it rainy and dark.

You do? Why?

It fits my insides. I have a place here now. I’m hoping to be bicoastal, as they say. I’m working on the other half of the buy.

And now you have awards season, so you’ll have to put that on hold. Going into Lincoln, what were you most fearful about?

I had no fears. I’ve been doing what I do for a very long time. You just say, “OK, this is what I’ve got to do, and you set about doing your work.”

How much research did you do?

As much as I could. I read the five real credible biographies on her. I read all her letters. I visited her childhood home. I went to collections—in Los Angeles and D.C.—of Mary and Abraham memorabilia. That’s the interior. Then there’s the exterior part of trying to match as much as I could with the pictures and documented evidence. They had measurements of what her waist size was when she was cinched in and corseted.

Did you get your waist as big as hers?

Yes, we accomplished that. Granted, I probably wasn’t cinched in as much as she’s cinched in. But I was cinched in a lot. At one point, I almost passed out! I put on 25 pounds to try to replicate her size. I went to a nutritionist, and I did it in a disciplined way. I felt like if it was just Sally going willy-nilly and eating chocolate cake, that would just feel like I had lost my mind.

Did you have fun doing it?

No, it was always disgusting. It was really revolting. I drank this stuff called Progain. That anyone would drink anything called Progain—bodybuilders do that. I would have that twice a day with nut butter. Ugh. Or I would eat these bars that the nutritionist gave me that were high caloric. And then I ate a lot of protein. I ate a lot of brown rice, nuts, and avocados. I didn’t really allow myself to have cheeseburgers and fries and all that.

I would have just eaten pizza all day.

I didn’t do that, either.

How about your wardrobe?

I had no makeup on. My hair took a while, because they put those heavy coils in the back. They built a tent for me for wherever I was, because I couldn’t dress in the motor homes. I’d wear every detail of what women wore in 1865. So many layers that nobody even sees, the crinolines and petticoats and the camisoles and the little shift that’s on underneath, and the pantaloons and the stockings. It just went on and on forever. And then you have to button up the boots. Going to the restroom was really interesting, too.

Because of all the layers?

I couldn’t get in the door!

You couldn’t!?

No. But I got good at it. I learned how to squish around.

Is it true that Daniel stayed in character during the entire shoot?

I did, too. I don’t know anybody who doesn’t really work like that. Daniel is just better at it. I’ve never tried to bring it out in the open, because I’m afraid people will think you’re strange. I’m too cowardly.

So you hide it by—?

By not speaking. Certain roles are lighter than others and you have to back off a little.

Did you stay in character on Brothers and Sisters?

We were always in character, even though that wasn’t a heavyweight thing. Those people still call me Momma. I was like, “Come on, you boys, I’m not your mother, for Chrissakes.” Rachel [Griffiths] still calls me Momma. I always had a hard time remembering their real names.

Some scholars believe that Mary was bipolar.

Well, they don’t really have the kind of research that would illuminate that. What you have is the documented incidents of how she behaved or the documented incidents that she was a big spender. She’d go on spending sprees.

What did she buy?

She bought tons of clothes. She had a gloves fixation.

In your interpretation she didn’t seem bipolar.

I don’t think she was. I see that she had a really difficult time with loss, and certainly the loss of her children.

Do you think Lincoln could have been gay?

I don’t know. Nobody knows. I know that Mary and Lincoln were extremely close, even though she was always haranguing on him like women do. There was some evidence early on in some letters that she was wishing that they were physically more together. She had a real appetite, sexually. And she needed him home. Certainly in the language of the era, they were much less homophobic. Men spoke of their friendships with men with such open-hearted devotion and love. Lincoln had an early friend, they wrote letters back and forth to each other. There wasn’t a problem with people sharing beds, either. There weren’t enough beds. When they would be on the lawyer circuit, you’d pick your bed partner. Mr. Lincoln had his favorites because Mr. Lincoln was big. And he wanted the little guys. Who knows what went on in those beds?

You know a lot about the period.

I did read a lot about that and the era. It did strike me as sad that we have lost the openness with our feelings of affection for people of the same sex, because we’re afraid.

When you were misquoted after winning your second Oscar, was it annoying?

It just forces me to explain it again. It gets boring.

Did it happen right away?

It happened right away. But I didn’t care. I was working. This is what I think about anyone that is critical: they can say whatever they want, when they win their second Oscar. I won’t criticize you, I promise.

When was the last time you went to the ceremony?

I don’t remember.

And this year, you will go as a nominee.

OK. Well, I’ll call you if I’m not. You’ll take me out to dinner.

If I’m wrong, we’ll get pizza.

OK. Good!