harry potter - Why would Hermione send for help from the trolls?

The main thing that trolls seem to be known for in Harry Potter, besides their love of killing/hitting things, is their stupidity. The lowest exam grade you can get is Troll, below Dreadful.

There are also numerous occasions in the books where trolls are mocked for being lumbering, brainless beasts without much intelligence or sophistication.

“How could a troll get in?” Harry asked as they climbed the stairs.
“Don’t ask me, they’re supposed to be really stupid,” said Ron.
_{(Philosopher's Stone, Chapter 10, Halloween).}

“Anyone can speak Troll,” said Fred dismissively. “All you have to do is point and grunt.”
_{(Goblet of Fire, Chapter 7, Bagman and Crouch).}

“And that complete cow Pansy Parkinson,” said Hermione viciously. “How she got to be a prefect when she’s thicker than a concussed troll ...”
_{(Order of the Phoenix, Chapter 10, Luna Lovegood).}

“You see what she’s up to? It’s her thing about half-breeds all over again - she’s trying to make out Hagrid’s some kind of dim-witted troll, just because he had a giantess for a mother..."
_{(Order of the Phoenix, Chapter 21, The Eye of the Snake).}

Leaving aside Hermione's blatant troll prejudice here, it's pretty self-evident that troll=idiot.

Which makes it odd when Hermione (acting as Minister for Magic) decides to seek them out to help the Ministry in The Cursed Child.

HERMIONE: We haven’t given up. We’ve gone to the giants. The trolls. Everyone we can find. The Aurors are out flying, searching, talking to those who know secrets, following those who won’t reveal secrets.
_{(The Cursed Child, Act 4, Scene 1).}

What possible indication could there have been that the trolls would a) entertain conversation or b) have any meaningful information for the Ministry? The fate of Barnabas the Barmy should surely be warning enough for any sane individual.

Furthermore, Aurors are highly trained magical spies. Neutralising angry trolls seems below their pay grade. Even if there was an emergency and Hermione was desperate it hardly seems like the best way of deploying her team.

Why did Hermione think that going to the trolls was going to be of any help whatsoever?

Answer

Trolls aren't brainless. The tie-in book "Fantastic Beasts and Where to Find Them" makes it abundantly clear that some trolls are smarter than others and some are even capable of carrying on a decent conversation.

As long as you can find an interlocutor who doesn't mind the possibility of being clubbed to death, they might prove a useful source of information on anything occurring in their mountain or forest territories.

Trolls generally converse in grunts that appear to constitute a crude language, though some have been known to understand and even to speak a few simple human words. The more intelligent of the species have been trained as guardians.

_{^{Fantastic Beasts and Where to Find Them}}

Indeed, some smaller trolls seem to have been sufficiently well trusted to be around children

...the Fat Lady was back. She had been expertly restored, but was still extremely nervous, and had only agreed to return to her job on condition that she was given extra protection.

A bunch of surly security trolls had been hired to guard her. They paced the corridor in a menacing group, talking in grunts and comparing the size of their clubs.

_{^{Harry Potter and the The Prisoner of Azkaban - – CHAPTER FOURTEEN: Snape’s Grudge}}