This is a repost. I believe I came up with a more refined translation.

I interpret "palmas" in the sense of "palm leaves", and "quartelas" as "corbels".

"Corbel: protruding architectural or decorative element, in the shape of a console, protruding from a vertical surface in order to support a sculpture, an arch, etc." http://www.conventocristo.gov.pt/en/index.php?s=white&pid=23... (Note: this website has a lot of terms related to church architecture.)

palma: [Botânica] Folha de palmeira. = PALMITO
"palma", in Dicionário Priberam da Língua Portuguesa [em linha], 2008-2023, https://dicionario.priberam.org/palma.

quartela: ARQUIT bracket, corbel: a projection from the face of a wall, supporting a weight. https://michaelis.uol.com.br/moderno-ingles/busca/portugues-...

Examples with both terms

"One of the corbels is quite plain, but the carving is crisp and well defined. I suspect it’s a replacement, installed at the same time as the 19th Century roof." From "Saints and Corbels" https://www.northbuckswanderer.com/2023/04/saints-and-corbel...

"A vase of flowers on a bracket near the picture of some dear one gone , or on her work-stand, or bureau, does not savour of idolatry." https://books.google.com/books?id=oUVDAAAAYAAJ&pg=PA429&lpg=...

Nossa Senhora das Dores: Our Lady of Sorrows

"The Friday of Sorrows is a solemn pious remembrance of the sorrowful Blessed Virgin Mary on the Friday before Palm Sunday held in the fifth week of Lent (formerly called "Passion Week"). In the Anglican Ordinariate's Divine Worship: The Missal it is called Saint Mary in Passiontide and sometimes it is traditionally known as Our Lady in Passiontide." (emphasis added) https://en.wikipedia.org/wiki/Friday_of_Sorrows

"Palm Sunday is the Christian moveable feast that falls on the Sunday before Easter. The feast commemorates Christ's triumphal entry into Jerusalem, an event mentioned in each of the four canonical Gospels. Its name originates from the palm branches waved by the crowd to greet and honor Jesus as he entered the city.[3] Palm Sunday marks the first day of Holy Week; in Western Christianity, this is the beginning of the last week of the solemn season of Lent, preceding Eastertide,[4][5][6][7] while in Eastern Christianity, Holy Week commences after the conclusion of Great Lent." https://en.wikipedia.org/wiki/Palm_Sunday

"É na festa de setembro
Popularmente conhecida
Que Jamacaru recebe
Os devotos da Mãe querida
Para saudar com palmas e flores
A nossa Senhora das Dores
A quem Jesus deu a vida."
(emphasis added)
https://jamacaru.blogspot.com/2011/09/jamacaru-terra-da-mae-

The following two paragraphs confim that "corbels" can be a part of an altarpiece (ES "retablo", PT "retábulo", not "retabolo"). https://www.aulete.com.br/retábulo

"There are six plasterwork corbels along the lower edge of the altarpiece, each with an angel holding a shield on it." https://www.churchsp.org/altarpieceretrospective/

Translated from Spanish: "The altarpiece, as an artistic manifestation, is a joint work in which carpenters, cabinetmakers, carvers, gilders, sculptors, painters, etc. have intervened, offering an ornamental, iconographic and pedagogical wealth, always under the gaze of the religious authorities." https://racba.es/retablos/

Corbel images (including a palm corbel): https://www.waddellmfg.com/collections/brackets-corbels-2/ty...

In conclusion, the palm has a special significance in Christian iconography. The representation of palm leaves on the corbels indicates the "victory" of Our Lady of Sorrows as a strong woman. As explained in the Wikipedia article, palm leaves were used to commemorate Christ's "triumphal" entry into Jerusalem. "Victory" and "triumph" are synonymous: https://www.merriam-webster.com/thesaurus/triumph

PS; Since the context provided is not enough to determine if "quartelas" are indeed "corbels", I'm leaving "brackets" as an alternative.

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Note added at 14 hrs (2023-12-17 03:50:38 GMT)
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If you wish to emphasize "palmas" in your translation, here's another option: The palm leaves [engraved/etched] on the corbels...