Très, Trop, Assez: Getting the Intensity Right
Très, trop, and assez describe intensity, each marking a different point on the same scale.
Très means « very, » a simple intensifier with no judgment attached. Trop means « too » in the sense of excess, and in French it almost always implies a problem, too much of something, to the point where it's no longer a good thing.
Trop almost never stands alone. Elle est trop fatiguée, on its own, feels incomplete, as if something's missing, unless it's answering a question (Elle peut nous rejoindre ce soir ? — Non, elle est trop fatiguée.). Without that context, the thought needs to be finished: elle est trop fatiguée pour voyager, not just elle est trop fatiguée.
Assez sits between the other two on the scale, « fairly » or « rather, » a moderate degree, less than très, and without trop's implication of excess.
Assez has a second meaning worth knowing too: « enough, » in the sense of sufficiency rather than degree. Same word, two different jobs, « fairly [good] » versus « enough [food], » and the only way to tell them apart is what follows: assez + adjective or adverb gives the « fairly » meaning, assez de + noun gives the « enough » meaning.
In casual, especially younger, spoken French, trop is often used as a plain intensifier with no negative sense at all, much closer to how English speakers actually use « too. »
Here, trop isn't marking excess, it's not saying she's nice to a fault. It's functioning as a casual intensifier, closer to « so » or « really » than to « too much. » The translation « too nice » would be wrong; « so nice » is what's actually meant.