As far as I know, Maria did not attend any church. Neither did her neice, Mabel, or her three children who were all close to their aunt since they all lived together at one point. Mabel's daughter's son, in his 70's now, remembered his grandmother Mabel's mother, Emma, and her sister, Maria, as two very sweet old woman. He recalled no other religion for any of them. He is not religious at all and couldn't discuss Russell teachings to save his life.
One of Mabel's sons, John, was given Maria's manuscript and Maria's favorite research books and Bibles when his mother knew she was dying. John also had the 7 volume WT Reprints and when he died, his son inherited his father's worldly goods including all of the books. That man told me that his father, John, did not go to any church, but he and his family attend the Baptist Church. Of any of the relatives I spoke to, this fellow has the most understanding of his Ackley and Russell background and their beliefs. And this is the man who gave me Maria's unpublished manuscript plus his father's WT Reprints and also Maria's personal study books and Bibles, which I will give to Princeton University to include in their Watch Tower collection.
Hopefully, I've answered the question asking if Maria attended any church. We don't have her saying so, but the evidence I think I've provided in this and my other post indicates she did not.
There were many people who left the Watch Tower religion after the divorce and after C.T. Russell's 1909 mediator-ship and new covenant change in teaching. It is thought the number was as high as 40,000. Out of this group, thousands were loyal to Maria and did not shun her. The people that shunned Maria were those who stayed loyal to Pastor Russell in the Bible Student movement. Also, Jehovah's Witnesses would not talk with Maria if they met her going door to door or if meeting a Bible Student under the same circumstance. In fact, a few years ago, Mabel's grandson in Florida went up to a JW engaged in street work in St. Petersburg and told her about his relationship to Maria Russell, which also includes a relationship to Pastor Russell. The Witness woman was very excited about meeting him and said she was going to tell the elders about him. The next time he tried to talk to her, she told him the elders told her not to speak to him. So even Maria's non-Witness, non-Bible Student descendants, over 60 years after she died, are shunned by JWs.