She served as a bridesmaid at the wedding of Alexandra of Denmark and Edward VII in 1867 and as Lady of the Bedchamber in the household of Princess Helena of the United Kingdom, who was the daughter of Queen Victoria.

[6] Queen Victoria attended a ball at Wimpole in October 1843 and wrote in her diary that "the 4 eldest [Yorke] Children appeared, very nicely dressed, and little Agneta looked so pretty.

[15][16] She later served as the Lady of the Bedchamber in the household of Queen Victoria's daughter, Princess Helena of the United Kingdom.

[6] Her funeral was held at St. Mary Magdalene Church in Brampton and she was buried in the Montagu family's private burial plot there.

[6] Queen Alexandra sent a floral arrangement of orchids, snowdrops, and violets in the shape of a cross, to the funeral, along with a message reading: "In fond remembrance of dearest Agnete Montagu, one of my oldest friends and bridesmaids.