Am I obligated to continue trying to please my husband's mother, who refuses reconciliation and mistreats me, even though I live far from my family and have no one else besides her, and she does not even ask about me when I am ill or in postpartum?

Responding to evil with good fosters affection and protects against the instigations of Satan, for Allah Almighty says: "Repel [evil] with that which is better, and thereupon the one whom between you and him is enmity will become as though he was a devoted friend." (Qur’an 41:34) Indeed, kindness and good words remove grudges and bring about love. If the husband's mother insists on estrangement after attempts at reconciliation, then there is no harm in avoiding her company until she calms down. The wife can ask her husband to introduce her to righteous women to alleviate her loneliness, and she should occupy her free time with what benefits her in her religion and worldly life, strengthening her connection with Allah through remembrance (dhikr) and supplication (du'a).