Depends on the meaning of "own". Quoting from https://www.mountvernon.org/george-washington/slavery/martha...
> After George and Martha Washington married in 1759, she took many of these people with her to Mount Vernon. As property of the Custis estate, they could not legally be freed or sold, and were inherited by the Custis heirs upon Martha Washington’s death.
In this case, Martha Washington owned the rights to the labor of the people involved until she died, but did not own the people themselves; the Custis estate did.
(Now what she would have done if she did own them outright is a separate issue, of course. Nothing suggests she would have freed them.)