She hails from a Minor Noble family, the Mordis'. I'm making all this up as I go, but they were wealthy through mining, particularly ore and precious gems, and made a killing selling the materials across the Alliance. Whether or not they were involved in Perenolds attempt to betray the alliance and join the Horde is murky at best, but their family fell into the national infighting at the end of the Second War. By the time the third war rolled around, they still had their lands as one of the last vestiges of "civil" society in Alterac, even so far as being a Barony with Baron Valimar Mordis as their family patriach who ruled with an even and steady hand...and then he fell to the scourge.
Marion was the eldest child and had been sent to Dalaran, but was lured away into the study of Demonology. With her family and national history, the teachers at Dalaran had 0 patience for her, so she had to flee, and she did, to Theramore.
As things are shaping up now, she has no living adults, and she is the oldest of (any) surviving siblings. She considers herself the heir to the Mordis' barony title, but is currently landless and penniless. When she gets her own estate again, she'll self-claim the title back, and then get to the business of having some kids. She's deliberately going to try and find a male of no station to marry, so that he'll be more inclined to take up her last name/heritage than his own. That way, via her plan, her family name is saved and restored.
At the moment, she's looking to try and get a good sized piece of Dustwallow Marsh, where she'll use her engineering know-how to drain it all and set up a bountiful farm/plantation, estate, warlock tower and engineering school.
She comes from a place that looks like:
Spoiler