Kesubos 9:6

If a woman’s husband died and she returned to her father’s house, or to her father-in-law’s house, and she was not appointed to administer the deceased’s estate, then her husband’s heirs cannot demand an oath of her. If she was appointed to administer the estate, then her husband’s heirs may demand an oath of her but only regarding future affairs and not regarding those in the past.

Kesubos 9:7

If a woman damages her claim to her kesubah (by saying that she already received part of it), she is only paid the balance upon taking an oath. If one witness testifies that she was already paid her kesubah, she is only paid upon taking an oath. If she seeks to collect the value of her kesubah from the property of orphans or mortgaged property, or in the husband’s absence (in a case of divorce), she is only paid upon taking an oath.