Maria is about 15-17 depending on her canon point. She's a student at the magic academy of the Kingdom of Sorcier, and the first commoner to be admitted in about ten years, due to her not only having magic (something extremely rare outside of the nobility) but her elemental affinity being light, which is the rarest element of all. Befitting her status as an otome game heroine, Maria is genuinely sweet, gentle, and hardworking, but a bit passive for her own good.
There are three timelines/canon 'verses that Maria can be taken from. While Maria's basic personality and backstory before attending the magic academy alter very little between 'verses, her relationships with the other characters, particularly Katarina Claes, are very different.
Hamefura Timeline/Main Timeline
This is the 'main' timeline that the primary manga, the anime, and the light novels all center around. In this version, Katarina Claes hits her head about eight years before she would normally meet Maria, and recovers her past life memories of being an otaku who was playing through the Fortune Lover game.
This means that the Katarina that Maria meets in the main timeline is a good-natured idiot who becomes friends with Maria and protects her from being bullied by the other noble girls. Maria is deeply in love with Katarina and through Katarina has become good friends with the other members of the student council, despite the other members also being love rivals for Katarina's affections.
Fortune Lover Timeline
This timeline isn't directly shown anywhere but the audience learns a great deal about it from Katarina's narration. In this timeline, Katarina Claes is a spoiled and selfish young woman who severely bullies Maria out of a mixture of jealousy and contempt for Maria's commoner origins. Maria has up to five potential love interests (including the Princes Geordo and Alan Stuart) but does not seem to have many friends due to being ostracized by Katarina and her social circle.
Verge of Destruction Timeline
This timeline is the focus of a spinoff manga series
As a result, Katarina's personality goes through a serious shift. She apologizes to Maria, stops bullying her, and begins to go out of her way to befriend and protect Maria from the other noblewomen. While Maria is initially wary, she warms up to Katarina over time and the two of them become genuine friends, although Maria does not seem to develop the romantic interest she has in the main timeline.