Mary is one of the co-owners of Downton Abbey — thanks to her late husband Matthew Crawley (Dan Stevens), who wrote her into his will before dying in a car crash.
After years of working alongside her father to manage the estate, the eldest Crawley daughter raised concerns about how it fits into an increasingly modernized world. The staff is leaving. The finances are tight. The damaged roof is expensive to repair.
"Are we right to keep it all going when the world it was built for is fading with every day that passes?" she eventually asks Violet, who counters her by saying that Downton Abbey will always be part of their family.
Shortly after, Mary asked her husband, Henry Talbot (Matthew Goode), if he's ever considered leaving it all behind.
"Leave Downton? I think we're stuck with it. Aren't we?" he asks her, to which she responds, "Yes. Yes, I believe we are."
At the end of the film, Mary stays at Downton Abbey with Henry, George Crawley (her and Matthew's son), and Caroline Talbot (her and Henry's daughter).