UsMagazine.com said the duchess' parents, Carole and Michael Middleton, are the first non-royals the queen has ever invited to join the holiday festivities.
Kate Middleton married the monarch's grandson, Prince William, in April 2011. She is pregnant with their first child and was hospitalized this month for severe morning sickness and dehydration.
Although she has said she is feeling better, the duchess won't finalize Christmas plans "until the night before or the morning of," an aide told UsMagazine.com.
"It depends [on] how she feels," the source said. "And if Catherine doesn't go, William probably won't either."