How should a daughter-in-law treat her husband's family who are abusive towards her in his absence, in an Islamic way that pleases Allah?

The correct Islamic treatment for the husband's family members who mistreat someone is to repel evil with good and to pardon them. This is a station that only the patient can attain. Allah Almighty says: "And not equal are the good deed and the bad. Repel [evil] with that which is better; then behold, he between whom and you was enmity [will become] as though he were a devoted friend. But none is granted it except those who are patient, and none is granted it except one having a great portion [of good]." The Prophet, peace and blessings be upon him, clarified that "Allah does not increase a servant in anything for pardoning except in honor," and that whoever pardons and acts kindly towards someone who wrongs him, it is as if he is feeding them hot ashes, and he will have a helper from Allah. This adherence will bring Allah's help and pleasure.