Mary Sue was just her facades.
To gain people's favour.
I mean, if one day she beat up some noble guy in secret, and the guy tattle to all other nobles, who do you think they will believe?
A normal noble guy or a very kind-sweet-rich MC?
MC is very forward with what she wants, and will pay double to those wronged her.
She also not very good with children since she have no experience around children.
Overall, I can say she definitely not Mary Sue type.
At least for now.

Does MC just stay being the flattest character ever? Idk if complexity is being lost in translation, but so far she just feels so mary sue ex machina.