Mary Cecil, 2nd Baroness Amherst of Hackney

In 1892, May's father, who by then had served several terms as member of the House of Commons became the 1st Baron Amherst of Hackney. As he had no male heirs, a special remainder granted that May (now known as Lady William Cecil) would succeed him as the 2nd Baron (i.e. Baroness) to pass the title on to her male heirs.[4]

In 1909, when her father died suddenly, Lady William Cecil succeeded him suo jure under the special remainder previously attained, as the 2nd Baron(ess) Amherst of Hackney,[14] but his residual estate had been reduced to £341,[15] as most of his personal collections and estate had been sold to pay off debt, when he was defrauded by his solicitor.[16][17][18]

Despite that it was unusual for women to participate in archaeology at the time,[19] in 1901, encouraged by Howard Carter, Lady William Cecil began excavations at Qubbet el-Hawa near Aswan. Her family was wintering in the area and while exploring on the west bank of the Nile had discovered what she thought might be an ancient cemetery.[20] Carter, who in 1899 had been appointed by the Antiquities Service as one of two European Chief Inspectors and in charge of excavations in the Nile Valley south from Qus to the Sudanese border,[21] came to see the find the following day. He arranged for permits to excavate and provided an inspector and workers to assist in the dig.[20] She kept a diary of the details of the expedition[22] in which multiple tombs were found, as well as wooden anthropoid coffins of the Saite Era. Though the entire necropolis was infested with termites, Tomb 21 yielded two burial boxes. The male's coffin disintegrated when it was touched, but the female's coffin remained intact[23] and was removed. The exterior was painted in yellow and devoid of any inscription. The mummy was covered with a blue network of beading. A coarse blue glaze was used on the winged scarabs and Amenti gods depicted on the canopic jars. The sole adornment of the mummy was a one inch by half inch opaque green stone. Lady William's diary recorded that the names found in the tomb were[24] Bao-bao, daughter of Pawebas and Shepentanefet and her brother Waher. She also reported remnants of a former burial, which may have been the tomb of Shepentanefret.[25]

In all, Lady William Cecil uncovered thirty-two tombs at the site which became known as the "Cecil Tombs", and were later called the Tombs of the Nobles[26] or Qubbet el-Hawa.[27] Her discovery of the tomb of Heqata was described as a small chamber, with two earthenware pots and containing a square coffin upon which were a bow and some arrow tips, as well as three walking sticks. Inside the coffin, on a trellis-shaped frame filled with grids of dirt, lay the mummy of Heqata.[28] The mummy was full of weevils, but was encased in seven layers of finely woven cloth. Though there were no artefacts found with the mummy, the exterior wrapping was painted white about the face with a painted necklace.[29] In many of the tombs, Lady William reported that they appeared to be re-used, and her finds suggest the artefacts came from a diverse range of dynasties.[30] The excavations proved successful and though Carter took "some of the best things", both he and Gaston Maspero were pleased with the endeavour.[22]

Returning home, Lady William Cecil published her findings "Report on the Work Done at Aswan" in the Annales du Service des Antiquités de l'Égypte in 1903.[19] In December, 1903, Lord and Lady William Cecil attended Princess Henry of Battenburg to return to Egypt,[31] having been members of her household for many years.[16][32] Her second season was not as productive and her work was overshadowed by a discovery made on Elephantine Island of a papyrus engagement contract. The document, in Aramaic script, contained important descriptions of the fortress and city of Aswan in the era of Artaxerxes I and Darius II[22] and Lady William worked diligently with Howard Carter and others to try to get it published.[33] In 1904, she published Bird Notes from the Nile,[34] which she offered for sale to benefit the parish church of St Mary's Church in Scarborough, North Yorkshire.[35] The book inspired the black crowned crane, balearica pavonia ceciliae to be named in her honour.[36] Other charitable works Lady William supported included the Children's Invalid Aid Fund;[37] London's Queen's Hospital for Children, for which she was one of only two women directors;[38] and the ambulance and hospital works of the Order of Saint John of Jerusalem,[39] for which she also served as a Lady Justice.[40] Lady William and her husband spent the next several years travelling, visiting Australia in 1905.[41]

In 1906, they were in Madrid, where Lady William served as the only English lady-in-waiting attending Victoria Eugenie of Battenberg, Princess Henry's daughter, when she became Spanish queen.[16] That same year at the request of the Empress Dowager Cixi, Lord and Lady William Cecil went with an English committee to help organise schools for Chinese girls.[42] They returned with Princess Henry and her entourage to Spain the following year, as well.[43]

During World War I, Lady Amherst participated in projects to raise funds for various war works, including an exhibition of her own paintings of Egyptian scenes at the Dudley Galleries[32] and a fundraiser at the Royal School of Needlework.[44] Her son and heir, The Hon. Captain William Amherst Cecil was killed at the Battle of the Aisne on 16 September 1914.[45] She was made an Officer of the Order of the British Empire (OBE) in 1919 for her charitable works with several governmental offices dealing with sanitation and health.[46]

Barely a month after her own mother died, Lady Amherst died on 20 December 1919 in London.[49] The coffin of Bao-bao was sold upon her death via a sale organised by Sotheby's in June 1921 to Albert M. Todd. In 1932, Todd presented the piece to the Kalamazoo Public Museum.[23] The Sotheby's sale was described as "the most important sale of Egyptian antiquities ever held in England" to that point in time and included 917 lots of Egyptian artefacts and 47 lots of cuneiform tablets and other objects.[50] Lady Amherst's journal on her first trip to Egypt is part of the records kept in Biltmore House in Asheville, North Carolina.[20] Her notes and letters have been useful references for other archaeologists in tracking provenance of objects which were part of the family collections[51] and because the tombs she inspected have not fully been subsequently explored.[52]