The distinction is that the first sentence grammatically says "at this moment you are a naughty girl" This is incorrect.
What you mean happens in this example: you see the girl all "dolled up" in her prom dress or something like that. Then, you could say
[Tú] Estás preciosa [con ese vestido] You look beautiful in that dress/ the dress makes you beautiful
[Tú] Eres preciosa You are beautiful - and the dress just remarks that
In your particular case
Tú eres una chica traviesa
indeed means "you are naughty", like in "that's inherent to you", but
Tú estás una chica traviesa
is plain wrong (it's a "word by word" translation, not a translation of the intended meaning). You would say
Tú estás traviesa hoy/esta mañana/en este momento
Tú estás preciosa con ese vestido/con el pelo recogido/esta mañana
You are translating literally "you are a naughty girl today" and that doesn't work in Spanish with "estar" because you'll say that someone "está traviesa/hermosa" but you don't say that someone "está una chica".
So you can say that someone "es una chica + adj", because that's inherent to them or a quality or a personality trait.
You cannot say someone "está una chica + adj", because "ella es una chica", and you could add that "ella es una chica hermosa, traviesa o alta, que puede estar más o menos -insert adjective here- en un momento dado".