I found this explanded story of Seattle nuns returning to the Catholic Church after decades as schismatics on the blog The Black Cordelias. The nuns who returned are now the Sisters of Mary Mother of the Church. I had known about this situation but did not know of the role of Mother Teresa's Missionaries of Charity:

"Last July, 15 nuns from a schismatic convent in Washington state rejoined the Catholic Church. They left the motherhouse of the Religious Congregation of Mary Immaculate Queen (CMRI), located on the outskirts of Spokane, to form a new congregation: the Sisters of Mary, Mother of the Church. They formally renounced their state of schism, made a profession of the Catholic faith, became a private association of the faithful under the care of Spokane Bishop William Skylstad, and recognized the legitimacy of the popes from Paul VI through Benedict XVI.
Their former order, which still has approximately 35 sisters, holds to the sedevacantist position that popes elected since John XXIII are invalid and that Vatican II was a heretical council. "

"In June of 2006, Sister Nirmala sent four of her sari-clad sisters to start a new foundation in Spokane and told the Missionaries of Charity novices to begin praying to Mother Teresa to help bring back the schismatic nuns of the CMRI order. There were exactly 32 Missionaries of Charity novices in the US at the time and 32 CMRI sisters stationed at the Mount. The novices’ prayers began to bear fruit.
Sister Alinda, the superior of the MC nuns in Spokane, went up to the Mount shortly after arriving. She continued to visit six more times in the first few months, after her arrival. On her last visit, the sisters at the sent her home with a large concrete statue of Our Lady of Grace for the garden of the MC convent. As she left the CMRI convent, Sister Alinda says she whispered to the Blessed Mother statue, “OK, I am taking you down the hill today, but now you have to come back here and bring the CMRI sisters down the hill with you."