She was governess to the children of King George III and Queen Charlotte for over thirty years, holding the position from 1762 to 1793.

Finch oversaw the princes' education until they became old enough to live in their own households under the watch of governors, while the six princesses remained under her supervision until they turned 21.

[6] William Finch had previously been married to Lady Anne Douglas, daughter of Duke of Queensberry but she died with no issue.

[10] Finch's biographer, Jill Shefrin, writes that the governess was noted for the skill she devoted to the raising of her own children,[2] while Christopher Hibbert suggests that her educated background made her "well suited" to the position.

[11] Lady Charlotte held the role of royal governess for over 30 years, and oversaw 14 of the king and queen's 15 children.

Fearing for her safety, she obtained a formal separation from her husband, taking their children to live with her in an apartment at St James's Palace and a house in Kew.

[2][14] However, when another of her daughters became ill in early 1767, Finch took leave of her job and brought the young girl to various locales in the unsuccessful hope she would survive.

Finch left the sub-governess Mrs Cotesworth in charge and returned grieving in November 1767, in time to care for the fifth addition to the nursery, Prince Edward.

[13] While the royal princes endured disciplined lessons in an austere educational environment, Finch was loved by her female charges.

An accomplished woman herself, Finch,[21] alongside Mrs Cotesworth, organised lessons in the arts and sciences which were taught to both the princes and princesses.

[24] Finch replied that she had regularly spent many hours with the princesses, both mornings and evenings, adding: How can I without deviating from my own principles undertake an additional duty of a kind for which I am conscious I am growing every day more unfit, as your Majesty must know what an uncommon stock of spirits and cheerfulness is necessary to go through the growing attendance of so many and such very young people in their amusements, as well as behaviour and instruction, besides ordering all the affairs of the nursery.

A new sub-governess, Martha Gouldsworthy (sister to Lieutenant-General Philip Goldsworthy, a favoured equerry of the king)[26]—hired on Finch's recommendation—now spent frequent time with the princesses, chaperoning and supervising their studies in preparation for their lessons with their teacher Miss Planta.

[28] In 1782, the 14th royal child, Prince Alfred, sickened and died at Windsor near the age of two, despite Lady Charlotte's devoted nursing.

[30] Finch resigned from her role in November 1792[30] and retired on 5 January 1793, though she continued to correspond with members of the royal family and receive gifts from them, particularly the Prince of Wales, the future George IV.

She received £600 in yearly payment, supplemented by income from the South Sea Company, until her death on 11 July 1813 at St James's Palace.