The Olympic champion suffered a semi-final defeat against Miku Tashiro of Japan, who later conceded to France's Clarisse Agbegnenou in the final.
In her bronze medal encounter, Trstenjak defeated Maylin del Toro Carvajal from Cuba.
Tashiro remains a kind of unsolvable riddle for the Slovenian judoist. Trstenjak, who has been beaten by her for the sixth time in as many encounters, said Takashiro "punished the single wrong step I made".
"I controlled the fight up to that point and she also did not show anything special," added Trstenjak, who has indicated that she is entirely focused on the 2020 Tokyo Olympics.
Her coach Marjan Fabjan is happy with the medal, praising especially Trstenjak's bronze medal match and arguing the goal had been met.
This is the fourth consecutive medal at World Championships for the 28-year-old Slovenian, who became World Champion in Astana in 2015 and won gold at the Rio Olympics a year later.