Red Herring Fallacy?

I don't know if this is a fallacy or not, but I feel like it is. Would using the concept of being a "good person" as an argument be a fallacy?

Example:

Kate: Bryson punched me earlier today

Linda: I don't believe you. Bryson wouldn't harm a fly/Bryson is a good guy.

I feel like it might be a red herring or some other fallacy, but, again, I don't know.

There are definitely issues with the logic in Linda's response. However, it can be argued Linda is just expressing an opinion (but this doesn't excuse poor reasoning).  When she says "Bryson is a good guy," she's not actually addressing the issue at hand—whether or not Bryson punched Kate. Instead, she's diverting the conversation by bringing up Bryson's character. This could be considered a form of ad hominem (abusive) , but in reverse. Instead of attacking someone's character to discredit them, she's praising someone's character to shield them. This doesn't actually provide any evidence to counter Kate's claim non sequitur . Plus, being a "good guy" is subjective and doesn't mean someone is incapable of doing something harmful ambiguity fallacy . So, Linda's argument (even if just implied) isn't a strong one and could indeed be seen as fallacious.

Another fallacy that can be applied is Argument from Incredulity.

Description: Concluding that because you can't or refuse to believe something, it must not be true, improbable, or the argument must be flawed. This is a specific form of the argument from ignorance.

Logical Form:
Person 1 makes a claim.
Person 2 cannot believe the claim.

Person 2 concludes, without any reason besides he or she cannot believe or refuses to believe it, that the claim is false or improbable.

I'd suggest Hypothesis Contrary to Fact or argumentum ad speculum:

Description: Offering a poorly supported claim about what might have happened in the past or future, if (the hypothetical part) circumstances or conditions were different.  The fallacy also entails treating future hypothetical situations as if they are fact.

Logical Form:

If event X did happen, then event Y would have happened (based only on speculation).

Alternatively, event X couldn't have happened because Y.

While it might seem as though there is good reason for Bryson not to have punched Kate, the fact is he did.

Just to add:
A red herring fallacy is an attempt to redirect a conversation away from its original topic.

Linda is not trying to do that, she just finds it difficult to believe that Bryson would have punched Kate because of how she perceives him and it's not unreasonable for her to find it difficult to believe Bryson punched Kate if he really is the good guy he seems to be but, ultimately, assuming Kate is telling the truth, it makes no difference what kind of guy Bryson is, the fact is he punched her.

It doesn't sound like a fallacy at all to me. I see two possibilities . . .

1. Linda really believes that Bryson is a good guy who wouldn't hurt a fly.

2. Linda is lying.