What is the fallacy when someone tries to claim that a commonly occuring phenomenom is an exclusivity or one off event.

What is it called when someone claims that widespread or common issue is exclusive to one particular topic, usually used to unfairly attack that topic in hand rather than attack the issue itself. I feel as if this fallacy is used to discredit or smear something someone has an animus against.

In real life context, often times, when I have tried to explain that any given phenomenon happening is ubiquitous and not exclusive to one event and try to use an example to to help (which might often help solve or lead to a solution, I often am met with the Strawman Fallacy and get accused of downplaying the severity which is not what I am really trying to do. 

Ex.)  news story about bullying at Smith high School. we know bullying a widespread phenomenon and it is bound to happen anywhere

Brenda: "Typical Smith High School, Terrible lazy teachers, bad students and rude parents, Of course it happened at THIS school" (Hasty Generalization / Ad Hominem (Abusive) )

Matt: " I hate to break it to you, but its not really a Smith High School Issue. My cousin attends Groveland High school and was bullied too"

Brenda: " Oh so you think its not a big deal because it happened somewhere else?"

Matt: "Not at all. I am simply saying that it is not exclusive to this school"  

Brenda: So you think bullying is okay?" (Strawman Fallacy)

Matt: "NO! Bullying is unacceptable period. no matter where it happens. In order to combat Its widespread occurrence we should press for more mental health funding, more counseling, everwhere, Not just attack the teachers & students at Smith High School"

Matt is not trying to downplay bullying. Matt also isn't trying to say that it's okay for bullying to happen at Smith High School because it happened elsewhere, he is simply implying that it is a prevalent issue and that the root cause of bullying could be traced to a variety of factors. Shouldn't we go after factors that may have caused bullying like improving mental health or discipline? etc.  rather than hasty generalizations and ad hominem attacks against The school?  Brenda while also against bullying, seems that her major argument here is to try and blame Smith High school exclusively, as if she has an animus against it, rather than attack the real issue at hand (bullying).

To end. the question here I am trying to ask is what fallacy would Brenda claiming a common, widespread event (bullying), is apparently exclusive? (happens only at Smith High School?)

Aside from the fallacies you correctly identified, I don't think there's a specific fallacy associated with claiming that trends are one-offs, this could simply be a factual error.

It sort of rings of the No True Scotsman fallacy to me. Here it feels like Brenda is asserting that bullying would not take place in a better school, when it in fact happens at every school because bullying is a sociopolitical tool used to force others into accepting the authority of the bully.

Similarly, Brenda is also confirming her biased judgement of this school's environment. And she is almost gaslighting members of this school into submitting to her authority.. by becoming a bully herself.