Lydia Mackenzie Falconer Miller or Harriet Myrtle (1812 – 11 March 1876) was a Scottish children's writer.

She was born Lydia Mackenzie Falconer to Elizabeth Lydia McLeod (d. 1865), a schoolteacher, and her husband, an Inverness-based merchant, William Fraser (1789–1828). She was baptised in 1812. After her father's business failed her mother's family helped pay for her education. She was schooled at Inverness Academy and later in Edinburgh, where she lodged with the musician George Thomson, a friend of the poet Robert Burns.

After some time in England she returned to Scotland, setting up a small school in Cromarty, where her family then lived. In Cromarty she met Hugh Miller. Both were well read and intelligent; she had lived in Edinburgh's literary society. Her family objected but they were engaged in 1832 and they married on 7 January 1837. Together they had four surviving children. Her husband was appointed to manage the periodical The Witness in Edinburgh and Lydia assisted and wrote contributions for the publication.

Under the pseudonym Mrs Harriet Myrtle, she wrote about 20 educational and moral stories for children which were often adventurous and light-hearted.