She had been expected to call in to the meeting with the Queen and Princes Charles, William and Harry about the Sussexes' decision to step back from senior royal duties.
In the end, the Sussexes decided it was not necessary for her to join the discussion, the source said.
The meeting was held at the Queen's Sandringham Estate in Norfolk, some 100 miles north of London, and Meghan is currently in Canada, with the couple's baby son Archie.
In a statement issued after the meeting, the Queen said the family would have preferred the couple to "remain full-time working members of the royal family," but that they "respect and understand" Harry and Meghan's "wish to live a more independent life."
The Queen has agreed to a "period of transition" while details of their new role are hammered out, the family announced.
Harry and Meghan will spend time in both the UK and Canada during this period. The couple revealed last week that they wish to step down as senior British royals and live part-time in North America.
The Queen said she had agreed that Harry and Meghan could split their time between the UK and Canada but that "complex matters" would have to be resolved. The monarch added that she had ordered final plans to be drawn up in the next few days.
Canadian Prime Minister Justin Trudeau told a local television station Monday that discussions are ongoing over who will pay the costs of the Duke and Duchess of Sussex's security for their proposed new life in the country.
Trudeau said "there is a general feeling of appreciation for the Sussexes" in Canada, but talks continue as to the exact arrangements.