I have trouble with two lines that are closely tied together. The following is them in context. The lines in question are shown in bold.
A: あなたは今、bla bla bla, irrelevant anime bs 状態なの…… そんな状態で暴れて回っても、 なんにもならないんだから……
The "irrelevant anime bs" is just me stripping the bit that explains B's situation in more detail, but that detail IMO would just lead us down the rabbit hole of explaining lore and like which is not the point here.
The following is my take on this segment:
A: Wait! B, I will arrest you!
B: You’re a nuisance…begone.
A: You are in a state of (irrelevant)… Because of that there is no point in getting violent, so…
B: I’ll be the one to decide whether or not there is any point. I won’t be interrupted by you.
A: Noo! I'll either interrupt you or fight you!
First of. For me it's strange that the verb 口を挟む is being used. As far as I can see it's used for interrupting someone's speech (like mouth is right there in the verb as object), while here from context B (which is suffering the interruption from A it seems) hasn't actually had her speech interupted. But more A is going to secure/arrest her and prevent her for going where she wants. And I don't really see in the definition of the verb it being used for this kind of thing.
Second thing is the 事じゃない which I'm not entirely sure what it's doing here. Is it, "it's not a situation where I'll suffer being interrupted", or general "I'm not/won't be interrupted by you" or something?
Due to the accumulated confusion, this makes the A's reply even more confusing to me. I know about the も～ば～も pattern that is used for and/or either/nor and such. So I guess she is saying she'll either interrupt/stop or fight her.