For my own interest, and compilation will be ongoing. Please feel free to add to the list via comments:
1) A Big Storm Knocked it Over by Laurie Colwin: Harriet aka "Birdie"
2) Tom's Midnight Garden by Philippa Pearce: Harriet Bartholomew aka Hatty
3) Harriet the Spy by Louise Fitzhugh: Harriet M. Welch
4) Harriet, You'll Drive Me Wild by Mem Fox: Harriet Harris
5) Garbo Laughs by Elizabeth Hay: Harriet Browning
6) The Lord Peter Wimsey mysteries by Dorothy L. Sayers: Harriet Vane
7) The Gates of Ivory by Margaret Drabble: Harriet Osborne
8) Harriet Bean series by Alexander McCall Smith: Harriet Bean
9) Emma by Jane Austen: Harriet Smith
10) Coventry by Helen Humphreys: Harriet Marsh
11) Sweetness at the Bottom of the Pie by Alan Bradley: Harriet de Luce (in spirit)
12) The Fifth Child by Doris Lessing: Harriet Lovett
13) "Harriet" (poem)by Charlie McKenzie: Harriet Michaels. (In the film So I Married an Axe Murderer, so this is a fictional literary Harriet).
14) Franklin the Turtle series by Paulette Bourgeois: Harriet the Turtle (Franklin's sister).