In the film, she exposes Dumbledore's Army to Umbridge while under the influence of Veritaserum, whereas in the novel the betrayal is willfully carried out by Marietta Edgecombe. Rowling has been criticised for perpetuating stereotypes of East Asians through Cho's name and shallow characterisation.
In the film adaptation of Harry Potter and the Order of the Phoenix, the character of Marietta Edgecombe does not appear, and instead it is Cho who betrays the D.A. under the influence of Veritaserum.
Shortly before Easter, one D.A. member, Marietta Edgecombe, betrayed them to Umbridge. She was a reluctant member of the D.A., having been brought to the meetings by her friend, Cho Chang.
During the latter conflict, no Slytherin students joined an association known as Dumbledore's Army; however, this could be explained by the fact that only those Hermione Granger, Ron Weasley, and Harry Potter trusted were invited.
Cho rats out Dumbledore Army | Harry Potter and the Order of the Phoenix
Why didnt Harry end up with Cho?
Their relationship grew stronger after the death of Cedric Diggory, but Harry suspected Cho of betraying their secret student group. Cho's lingering feelings for Cedric and a lack of chemistry between her and Harry contributed to their breakup, leading to Harry ultimately ending up with Ginny Weasley.
For example, Peter Pettigrew was in Gryffindor, yet he betrayed the Order of the Phoenix and joined Voldemort; Quirinus Quirrell, a Ravenclaw, also allied himself with the Dark Lord; and (albeit only in an alternate timeline) Cedric Diggory from Hufflepuff would become a Death Eater, whereas Slytherins such as Horace ...
If you have only seen the films, you might be surprised to hear that it wasn't Cho Chang who betrayed Dumbledore's Army to Professor Umbridge – it was Marietta Edgecombe. A friend of Cho's and a fellow Ravenclaw, Marietta (reluctantly) joined the DA.
In the books Cho Chang is older than Harry by 1 year, in the movies Harry and Cho are both in the same year. By the last book, Cho and all the other members of DA came back because Neville send them a fake galleon they use to communicate to call the others.
She survived the war and eventually married a muggle Mr. Campbell and had a daughter named Erin. Even though Cho seemed very innocent and kind, she still couldn't get over the fact that Cedric Diggory was dead and Harry Potter, her new crush, had been right beside Cedric when he died.
Cho didn't like Ron Weasley and Hermione Granger; she believed that Harry had romantic feelings for Hermione, instead of being friends. This was one of the reasons that Cho and Harry fell apart. However, she fought with Dumbledore's Army during the Battle of Hogwarts, and the most of them survived the war.
Back in 2007, J.K Rowling revealed Cho's fate during a Q&A session in New Orleans. Here, the author confirmed that Cho had survived the battle and had gone on to marry a muggle (a non-magical person).
In the books, it was Cho's best friend Marietta that betrayed them. She was not coerced. Instead, she went to Umbridge and told her about the D.A. and where they were meeting that night. If it wasn't for Dobby, they would all have been caught red-handed.
In the film adaptation of Order of the Phoenix, Marietta does not appear and her betrayal is instead committed by Cho, under the influence of the Veritaserum potion. A Muggle-born student in Harry's year.
What she hadn't bargained for was the hex Hermione Granger had cast on the very sign-up sheet itself, designed so that anybody who betrayed the trust of the Army would immediately break out in painful, ugly spots on their face, aptly spelling out the word 'SNEAK'.
Despite all three champions being chosen, the Goblet of Fire nominates Harry to become the fourth Triwizard Champion. Cedric remains kind to Harry whilst everyone else assumes Harry is lying when he asserts that he did not put his name in the Goblet of Fire.
He fell for her in his third year of Howarts. At first, Cho does not return these feelings for him. However, she still treats him with respect, by refusing to wear the "Potter Stinks shirts Malfoy made. In Cho's sixth year, following Cedric's death, Harry comforts Cho, and the two kiss.
Apparently, Umbridge's mother was a Muggle and her brother was a Squib – a source of huge embarrassment for the family. Perhaps their abandonment and retreat back into the Muggle world had such a huge impact on Umbridge that it became the catalyst for her Muggleborn-targeted cruelty later on in life.
He sobbed openly when he saw Cedric had died and when he was interviewed about his son's death, but at least didn't blame Harry for it, and contrary, believed Harry's claim of Voldemort's return and thanked him for returning Cedric's body.
Although Umbridge was not a Death Eater, and had no direct contact with Lord Voldemort, she showed that she was fairly in line with their goals. This was due to Umbridge's callous nature and her prejudiced beliefs, both of which were similar to Death Eater behavior.
Professor Lockhart is the best - or rather, worst - example of these bad Ravenclaw traits. He has spent his entire career using magic to take advantage of other people, and thus, take credit for their knowledge.
Peter Pettigrew (a.k.a. Wormtail) is one of two Death Eaters known to have been in a House other than Slytherin (Gryffindor) while at Hogwarts. There, he was a close friend of Sirius Black, James Potter, and Remus Lupin, although he was the least intelligent and least talented of the group.
Ominis Gaunt was a part of Slytherin house during his time at Hogwarts School of Witchcraft and Wizardry. This was a house he expected to be sorted into due to his heritage.
