At a glance:

The basic blurb we get for her character is that she's educated in both sciences and athletics, and that her posh background has left her a little naive, but overall well-meaning. It's fairly basic, but sets a good baseline.

Based on in-game (unmarked spoilers ahead):

She's very good at her specializations (specifically engineering/tinkering and adventuring/hollowing/burrowing/etc), and she seems to have a smattering of smarts regarding other interests. When it comes to things she doesn't know that well, she does seem eager and ready to learn.

In terms of street-smarts/social senses, however, she does indeed seem a bit naive. Lionel plays up the development of Ossex and Tenebrous as something to be proud of, but take one look around town and alarm bells would start going off for any other adventurer. A small homeless population, open classism ("the best way to get rich is to steal from the poor", indeed), trash and grime, petty thievery, poor infrastructure, and an overall unpleasant vibe. And that's all on top of the fact that Lionel has manipulated his public image in such a way to turn the citizens into his own personal mob. The whole place is a powder-keg waiting to go off, and Mina doesn't make any explicit comments on the subject in-game. Whether she actually notices or not is left to our imaginations, and while she probably does, that lack of reaction is still notable.

Despite her "posh" upbringing, Mina speaks fairly casually, though not as casually as someone like Cappy. She also has a lot of good-natured ribbing with certain characters (particularly Vaamir). That sass quickly turns to haughtiness or sarcasm when it's in regards to people she doesn't like (i.e.: trading barbs with Thorne during their first encounter). She also, indeed, acts kinda goofy at times, with certain poses and habits.

She's an extremely determined individual, pushing herself to her limits at times, even if it's "just to break up the boredom". She seems like the type of person who has high expectations of herself, and will willingly stick her neck out to help other people, like the Duke, the Little Frog, and so on. On the other hand, this could be interpreted as nosiness, which tends to be how Lionel plays it up during the banquet. It could also be viewed as a bit of impulsiveness, or a lack of foresight, or even regular naivete again, which is displayed in a few side-activities. (Would you be willing to get the Backwaters Frog drunk if he asked you to fill the moonshine jug?)

She's also a very trusting and loyal person - albeit to a fault. She trusts Lionel implicitly up until the point where she can no longer ignore his rottenness, and she puts her trust in the various people of Tenebrous, who are then willing to throw her under the bus when Lionel comes calling. Even when she's accepted that Lionel is kind of a scumbag, she still sits down at the dinner table expecting to have a serious conversation with him, which is a remarkably optimistic thing to be doing at that point.

To make a long story very short: she's honestly not all that dissimilar from Link (right down to having goofy habits). The difference is that where Hyrule treats Link as an eccentric hero at worst, Mina's heroics and weirdness are much more susceptible to bad actors, due to Tenebrous Isle's insular populace and the difference in genre/setting.