What makes you think that those in heaven are dead? Only God and those in Heaven knows where Mary is. There is no doubt some saints have been raised for Gods purposes.We know Abraham, Moses and others have been raised as surely as there are many who have not been.
1Thess. 4:16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first.
Aren't the angels' salutation "Hail, Full of Grace" (ore "Most Highly Favored") and Mary's embrace of her Savior ("My spirit rejoices in God my Savior") and her inspired declaration "All generations will call me blessed" and her reception of the Holy Spirit, together with the Apostles, at Pentecost, clear
assurances that she's one of God's holy ones, i.e. she's "saved"? Therefore in heaven??
Are there any grounds to doubt?