The star, who is in town to receive a Donostia Award for lifetime achievement as well as to promote Bayona's feature, also wasted no time in voicing support for Democratic presidential candidate Hillary Clinton.
She said: "As women know, we are strong and we are the glue that holds our world together. It's very exciting in the US now that, in spite of ups and downs, we're finally going to have a woman president. It's way overdue. I think that a lot of the progress that we've made is now coming to fruition and we have women in all walks of life."
Weaver - who adopts an English accent for the role of a grandmother who has to take care of her frightened grandson after his mother goes into hospital for cancer treatment in A Monster Calls - added that the changing landscape for women was also leading to more roles for them on film.
She said: "I don't think I've ever had more work. I think men have more roles but I don't think they have better roles. I don't sit around envying Russell Crowe his roles - and I think he's a brilliant actor. I think being a student of literature, great stories have great women's parts.
"I think there was a period when, especially in comedy, there was a temptation for writers to write grotesque women relatives and things like that, all of which I avoided. But I feel that now because our landscape has changed and women are in the world playing in real life CEOs, politicians and the head of the International Monetary Fund and all these things, women are in our lives in a very high-profile way and I feel that's very much reflected in movies. I'm often asked to play roles that would have traditionally gone to men but now go to me because that's the way our world has changed so I think it's a very good time for women.
Weaver in A Monster Calls: Jota is like a volcano of ideas' Photo: Courtesy San Sebastian Film Festival
Weaver first attended the festival in 1979 with Scott's Alien and says she remembers the trip "vividly". Speaking about Chappie director Neill Blomkamp's sequel to the film, she added: "We had to postpone. He has work to do and I have various things going on. I hope we do get to do it. It's one of those things where we would have loved to do it this past year but I think Ridley Scott didn't want all the movies to come out at the same time [Scott's Alien: Covenant is due for release next year]. I think that's very smart."
The 66-year-old also recalled going to see The Beatles as a girl - a snippet of film that has been captured in the recently released The Beatles: Eight Days A Week - The Touring Years. Correcting reports that she was 14 at the time, she said: "I'm 11 in that film, even though I'm eight feet tall, it was a big night for me. I went by myself and I was surrounded by all these weeping women and I was just so excited. Every now and then I'd scream just to be part of it all."
Weaver also talked about the string of "extraordinary directors" she has worked with during her career.
She said: I don't know how I got so lucky. I learned so much, especially in the beginning, from Ridley Scott and from Peter Weir especially. Weir helped me to understand how to surrender to the chaos of film because I was from the theatre. It was always to me it was about the story but second, and very important in film, was to work with a director who had a very strong vision and who was a fighter who could make that vision come to pass because all kinds of things can happen on a film that can try to undo your work. You have to have a very strong director who will get you through that. So I feel very fortunate.
"I think Jota is right up there with Fincher. He's extraordinary and, to me, he's his own director. I wouldn't think of comparing him to others because to me his talent is unique. It's very Spanish - filled with a lot of passion and confidence and honesty. The connection he makes to material is very instinctive. Fincher is brilliant but his approach is more intellectual. Jota is like a volcano of ideas, it's amazing for me in such a young man to find such confidence. That's very reassuring to a cast when they're dealing with such challenging material that you have to present to the audience in a deeply honest and sincere way. He was definitely the captain of our ship and we felt in very good hands."