The authors' Dr Ruth Galloway series include the Woman in Blue and the ChalkPit, will give fans the chance to name a character in her next novel The Stone Circle.
Get in Character
is a unique seven-day eBay auction
that runs until Sunday 4th March 2018, with proceeds going to supporting children and young people with cancer and their families.
Elly has supported Get in Character since its formation and has a personal connection to the cause as a family friend tragically lost her life to cancer a couple of years ago.
Elly said: "I'm really am proud to be involved once again and to continue to support such an important cause that is close to my heart.
"CLIC Sargent came to my attention through my love of books when an author pointed out their auctions a couple of years ago.
"I was amazed then and since, by the number and quality of novelists that have offered book characters or writing support."
Over fifty authors are taking part this year in the campaign which has raised almost £35,000 for the charity since it began in 2014.
Other authors taking part in the Get in Character auction include internationally acclaimed thriller writer Peter James, crime writer Christopher Brookmyer and Sarah Hillary.
Other items that will be auctioned during the event include signed books from Graham Norton, Ian Rankin, Clare Balding, Charlie Higson and Lee Child, as well as a signed one off illustration from Axel Scheffler (The Gruffalo).
The campaign also offers one lucky applicant the chance to win a signed War Horse book from family favourite Michael Morpurgo, along with a live experience in London.