Limbus fans mistakenly think Don is stupid. Don is really smart she's just operating on a different wavelength than everyone else.
In many of her Mirror World IDs she's either the director of a whole Section or moved up the ranks very quickly. She picks up the symbols on Mephistopheles and deduces which door they lead to (the plan was ill-advised but still). She's incredibly well-versed in Fixer lore and could talk for hours about them. (How many Fixers are there?) Her LobEGO ID shows she's competent at handling some fairly dangerous Abnormalities and containing them.
But she also wants to hug the Abnormalities and eat raw chicken and once tried to make a chicken dish with chocolate and orange. She stabbed Ryoshu because she was being senselessly violent. She made a pretty detailed account of the Steam Engine Abno's ability to boil her eyeballs.