It is uncertain what had happen to Melenor during the attack on Altea by the Galra Empire. It can only be assumed that she had perished along with many Alteans after the destruction of the Planet Altea.
Melenor has a stunningly similar, if not clone-like, appearance to her daughter, Allura, who was mistaken for Melenor in Season 8 by the Spirit of Zarkon after their initial battle in Honerva's mind. She was a tall woman with brown skin, white long hair that is done in a similar style to Allura's, Like all Alteans her ears are pointed rather than rounded and has small pink sickle-shaped marks situated on her cheekbones, one under each blue eye.
Melenor wore a crown similar to Allura's and the same earrings on her ears, it could be hinted that Allura's jewelry may have been passed down by her Mother. She wears a pink dress trimmed with gold with what seems to be a white shirt layered underneath.
Before the Altean Genocide
Not much is known about Melenor before the fall of Altea. She was seen only briefly a few times in the show. She was there with her husband Alfor on Daibazaal having a friendly dinner with Zarkon and Honvera and was even present at their wedding. This could mean that she could have had a deep friendship with the two, much like her husband and was there with the Trans-reality Comet had struck Daibazaal.
Melenor was also there in the memory of when Zarkon was first introduced to a young baby Allura, and had gifted her a helm. After that the whereabouts of the Queen are unknown.
Melenor is only ever seen within memories, often told by Coran. He seems to recall her and King Alfor with deep fondness and sadness. And although Allura's thoughts and memories centered around her father for most of the series, towards the ending of Season 8 Allura dreams of her mother on Altea who is smiling at her and stating that she was proud of her. Though Melenor did not make an appearance along side her husband during Allura's ultimate sacrifice.
Most of the Queen's personality is unknown. She seems light and cheerful, more quiet and serene than her husband and can be as regal as a Queen should be. She was very kind and loving to her family, though we do not know how she was as a Monarch along side her husband who chose to serve the People than to rule much over them. She may have shared the ideals of Alfor and most Alteans, pushing towards peace and diplomacy though she was not a fighter.