Naive, yes, stupid maybe. She may lack a bit of common sense, but overall I'd say she does display some sort of intellect. You're right though, definitely not smart when it comes to the being a drug dealer. She maybe wasn't at first, but as her ambition grew, so did the depth she was in and now she's out of her depth.
I wouldn't say she is winging it. In the first instance Maya is a prime candidate for the restaurant "free tuition" program. Here we have a somewhat naive girl desperate for money, who in her first test was willing to compromise on her priciples and "seduce" the MC, as time goes on its clear that where as Maya may do anything for that tuition there's some lines she won't cross, did Quinn misread maybe... But she also gave a list of what she thought was impossibleish tasks, was this her way of ensuring Maya never made it as a hot?
This I can agree with, she definitely thinks she's the smartest person in the room. And even on occasions she's humbled still refuses to backdown and in some cases doubles down. This is more arrogance than stupidity. (though it is a bit of both)
To me quinn is a somewhat naive girl who overestimate smartness, she's definitely not as good a manipulator as she thinks she is and her own arrogance is the cause for a lot of her problems. It might scream stupidity I grant you, but also, it was working for a bit so there is at least some levels of smarts there