A former employee to Danielle Steel has admitted she stole at least $400,000 US from the bestselling American romance novelist.

Kristy Watts, who also goes by the name Kristy Siegrist, worked for the prolific Steel from 1993 through 2008 and was in charge of financial matters, including bookkeeping, payroll, accounting and co-ordinating household and travel expenses, according to a statement from U.S. prosecutors.

Watts has admitted embezzling from Steel between 2003 and 2008, by depositing cheques into her personal bank account and using the famed author's credit card reward points to purchase items for herself and her family.

Watts, 47, concealed the fraud by falsifying accounting records and understating her income, said a statement from U.S. Attorney Joseph P. Russoniello.

After pleading guilty to one count of wire fraud and four counts of tax evasion, Watts is to be sentenced in federal court in San Francisco on Feb. 4. She faces significant prison time and fines.

Despite publishing dozens of books — from her best-selling romance novels to non-fiction titles and tales for children — Steel, 62, has long been reclusive and extremely guarded about her personal life.

With files from The Associated Press