The Shining was adopted from a classic Stephen King novel and took some creative liscences to make it into its own thing entirely. It was so different that Stephen King said he hated the adaptation. Critics followed along and shytted on it too, not really seeing what made it anything other than an incoherent run of the mill ghost story. But through the years people have rewatched it and noticed the shytload of details, symbolism, and imagery Kurbrick put into the film and it has since become adored.
Grace is saying Batman V Superman is for comic book movies what The Shining was to horror films, a misunderstood masterpiece that people will come to love later.