The singer and vocal coach opened up to PEOPLE in an exclusive interview about the barrage of criticism she faced following her performance at a baseball game.

Cassie Donegan was thrilled for the opportunity to perform the patriotic anthem God Bless America at the Major League Baseball (MLB) All-Star Game in Philadelphia.

"To sing that song as Miss America, on the nation's biggest sporting stage, and in the year of the U.S. Semiquincentennial—I was absolutely overjoyed," the 28-year-old tells PEOPLE. "What made it even more special was having my dad there in the stands. As a disabled veteran, he was able to share that joy with me."

However, just an hour after the performance, short clips of her appearance began circulating on social media accompanied by a wave of venomous comments. Users began attacking her weight, makeup, age, and even questioning her gender.

"In my entire life, I could never have imagined that a 10-second clip would lead to hundreds of people commenting and DMing me to 'do the world a favor and kill myself' so they wouldn't have to look at me anymore," she admits. "It was brutally harsh."

Donegan, who has been making regular public appearances since winning the title, admits she still doesn't understand what triggered such an outburst of hatred.

"I have no idea. I wish I could figure it out, but I genuinely don't know. Prior to this, I've had the honor of singing at equally massive venues in front of huge crowds, and it never drew this kind of negativity."

At first, Cassie tried to simply ignore the attacks—until the cyberbullying started affecting her students.

One of her 13-year-old students, who dreamed of a career in musical theater, candidly asked her teacher if she should even bother pursuing it. After seeing her mentor get "destroyed online," the young girl fearfully asked, "What are they going to do to me?"

"That was the moment I realized I had an absolute obligation to speak out. This had grown far beyond a personal issue," Donegan says.

On July 15, Cassie posted a response on Instagram, calling the harassment "the most malicious and vile content" she had ever witnessed. "Right now, somewhere out there, a young girl is watching how society speaks about women," Donegan wrote. "And based on that, she's learning how to view herself."

Speaking with PEOPLE, Cassie emphasized: "The absolute last thing I want is for a young girl, a woman, or anyone at all to look at those posts and conclude that they need to change themselves or fit into some conventional mold of beauty just to earn the right to pursue their dreams. When a woman's appearance becomes the subject of public mockery, those words don't just hurt her alone. Every girl and woman absorbs them."

Reflecting on her decision to take the story public, Miss America explained her reasoning: "I didn't speak up to get an apology," Cassie concludes. "I don't need one. And I don't need the haters to suddenly change their minds and think I'm beautiful or talented. I just hope that the next time they have the opportunity to tear someone down, they make a different choice."