They do get into her family later in the story (and after that point, it comes up A LOT) but she is not royalty.
Since nested spoiler tags don't work, so if you don't want to know more don't read after this line:
Her mother was a top consort at the place she grew up, and her father still is a high ranking general in the army. Who is perhaps even more eccentric than Maomao is. It's hereditary.