If certain human relationships such as marriage end at death, and spouses are not our spouses any longer when we are in heaven (cf. Matt. 22:23-30), are our mothers and fathers and children still our relatives in heaven? I’ve seen this argument used to show that Mary is no longer Jesus’ mother in heaven.
In his answer to the Sadducees, Jesus’ point was that marriage is an institution intended to serve only this present life. It gives the spouses a road to holiness and enables them to raise up new human beings for the heavenly kingdom. Because those purposes will have been fulfilled in the next life, there will be no need for marriage in eternity.
That does not mean that other relationships are similarly cast aside. It does not even mean that a husband and wife will not have a special relationship in eternity of which we cannot now fathom. In fact, the parents of St. Therese of Lisieux, Louis and Zelie Martin, are currently being considered for sainthood and the Church has encouraged that those who pray for their intercession pray to them as a couple, in order to better emphasize the sanctifying power of the sacrament of matrimony that strengthened them in this life.
A mother is always a mother, given the nature of her special bond with her child. There is no reason to believe that this is any different with the relationship between the Blessed Virgin Mary and her Son, Jesus Christ.