Is there a sect (dissenting or schismatic) of Christians that believe in the divinity of Mary, Mother of Jesus?
Collyridianism was a movement in the 4th century in Arabia which is said to have taught that Mary was a goddess. We know little about them however, and they are mentioned in only one contemporary source by Epiphanius of Salamis.
I don’t know if the World Mission Society Church of God (South Korea) qualifies, but they have ascribed divinity to the wife of the founder of this cult.
The WMSCG was founded by Ahn Sahng-hong in 1964. He was supposed to be the second coming of Christ. Ahn Sahng-Hong died in 1985 leaving the leadership of the church to his spiritual wife, Zahng Gil-Jah, known in the church as "the Heavenly Mother". The General Pastor, Kim Joo-Cheol. Zahng is also chairperson of the’ New Life Welfare Foundation’ and of the’ International We Love You Foundation’. The church believes that Zahng Gil-Jah is God the Mother:
On a meeting in Seoul on 2 June 1985 two major new doctrines were codified:
Ahn Sahng-hong should be regarded as Jesus Christ who had already come, should be titled Christ Ahn Sahng-hong, and pursuant to a traditional trinitarian view of Christian hypostasis, Ahn was consequently also The Holy Spirit, God the Father, and thus God.
Zahng Gil-jah should be regarded as God the Mother, a female image of God, be titled Heavenly Mother, or simply Mother, and together with Ahn Sahng-hong be regarded as God.
Source: World Mission Society Church of God: https://en.wikipedia.org/wiki/World_Mission_Society_Church_of_God#History
I realise that calling this woman God the Mother is not the same thing as saying Mary (the mother of Jesus) is divine. It's much worse.
Divinity or the divine are things that are either related to, devoted to, or proceeding from a deity. What is or is not divine may be loosely defined, as it is used by different belief systems.
The root of the word divine is literally godly (from the Latin deus, cf. Dyaus, closely related to Greek zeus, div in Persian and deva in Sanskrit, but the use varies significantly depending on which deity is being discussed. Source
A divinity is a religious being, like a god or angel.
Mary is higher than all the angels combined is the teaching of the Catholic Church. Is Mary Divine? No, She is not God.
492 The "splendor of an entirely unique holiness" by which Mary is "enriched from the first instant of her conception" comes wholly from Christ: she is "redeemed, in a more exalted fashion, by reason of the merits of her Son".136 The Father blessed Mary more than any other created person "in Christ with every spiritual blessing in the heavenly places" and chose her "in Christ before the foundation of the world, to be holy and blameless before him in love".137
Is Mary Holy? The Catholic Church both Eastern and Latin Church teaches Mary is Panagia or All Holy.
493 The Fathers of the Eastern tradition call the Mother of God "the All-Holy" (Panagia), and celebrate her as "free from any stain of sin, as though fashioned by the Holy Spirit and formed as a new creature".138 By the grace of God Mary remained free of every personal sin her whole life long.
Is Holy the same as Divine? In some ways, Holy is synonymous to being Divine. It means the fullness of God resides in a soul, but in Mary's soul, it does not only resides, but the term is mystical union.
If we based our understanding that Divine and Holy are synonymous, then the Catholic Church by accepting the teachings of St. Maximillian Kolbe on "quasi-incarnation", then Mary attained "divinity" because the Holy Spirit fully resides in Her whole being mind, body, and soul.
St. Athanasius said these words: "God became man so that man shall become god/divine."
We are all called to be perfect like the Father who is Divine, and in the process called Theosis, man can attain divinity like God.
Did Mary attain divinity? Her words of revelation to St. Bernadette Soubirous affirmed it, "I AM the Immaculate Conception. The Word "I AM" is Divine and Mary claimed this as Her own in the Our Lady of Lourdes approved apparition.
The Catholic Church never teaches Mary is Divine, but St. Maximillian Kolbe's teaching on "quasi-incarnation" has presented Mary as attaining "divinity" by Her perfect and complete mystical union with the Holy Spirit being Her beloved Spouse.
Quasi-incarnation can be described like this.Mary speak the word "I AM" the Immaculate Conception which is Divine. St.Kolbe, defined this "Divinity" as "quasi-incarnation". If Mary enflesh Jesus to dwell among us. With the Holy Spirit, Mary gave Her very own body, mind and soul to the Holy Spirit, it is like a "total possession or complete union". As if, if one sees Mary, it is actually the Holy Spirit operating in Her very being, all Her thoughts, words and actions are all coming from the Holy Spirit. And, St.Kolbe could not find a words to describe it, and so the "quasi-incarnation" of the Holy Spirit is the closest that he can describe. Mary's whole being personifies the Holy Spirit. The Holy Spirit speaks the word "I AM" in Her being, when St.Bernadette Soubirous asked Her, "Who are you?", and She answered, with a revelation that the Holy Spirit is present in Her whole being, saying the words, "I AM the Immaculate Conception".
More on "quasi-incarnation".