What are the fights about?

Obviously you let her get away with it.

You're failing to understand her. Emotionally.

If she feels insecure because you have female friends arguing or having a logical debate on why she shouldn't won't do much. Yeah it will make sense to her but guess what, she's still being toxic because she still feels the same way.

Try relating to her on an emotional level for a change. Let her know that you understand why she would feel that way, but you're a guy that has female friends. That's who you were before her and it's who you'll always be. But then there's a reason why she's your girlfriend and they're just friends.

So whenever we get into a fight, I somehow manage to sort things out and reach a verdict that favor both of us.
But
Even though everything's been sorted out and I ask her if it is and she says it too. Well I feel it isn't
Because
she still is in that standoffish mood, she carry's that toxicity throughout almost ranging on to a couple of days.

Now I have talked to her about her behavior, she too knows its bad but she gets all defensive and says "That's the way I am, why can't you love me the way I am

What should I do........

Should I let her carry the toxicity around and let it die out or should I try to change her...

Or any other course of action ?

It's the same thing. You may know what the problem is but are failing to express your understanding, hence she doesn't feel understood.

The problem with these female friends are, I used to be an guardian angel for them. Any problems they had, that were too much,they came to me to sort it out... So one of these girls was having a breakdown due to her periods, she was talking to me about her x and how she still loves him etc..

That moment simultaneously I was talking to my girlfriend and she asked what I was doing and I told I was "helping x girl out, she got her periods now she's going to be annoying..."

So my girlfriend is like so hellbent on the periods thing, she's like how the fuck is she so close to you that shes telling you she's having her periods etc etc.

I think it's coming more from a jealousy pov, cause she is someone who really wants attention but she's shy to tell, she doesn't want to be judged etc,she won't express it.