[Goatus]

hmm don't know if found your bug already but i will try answering

From what i can see you call PetWindow_Update (which is responsible for showing hidding your frame) only OnLoad for your frame.

function PetWindow_OnLoad()
	
        [cut]
	
	this.attackModeCounter = 0;
	this.attackModeSign = -1;
	--this.flashState = 1;
	--this.flashTimer = 0;
        PetWindow_Update();
	CombatFeedback_Initialize(PetHitIndicator, 30);
	
        [cut]
end

But OnLoad happens much earlier then UnitExist("pet") returns true so it won't show... You should call PetWindow_Update at least on event: "PLAYER_PET_CHANGED"

here:

function PetWindow_OnEvent()
	PeW_OnEvent(event);
	if ( event == "PLAYER_PET_CHANGED" ) then
		PeW_Update();
                PetWindow_Update();
		return;
	end
	if ( event == "PLAYER_ENTERING_WORLD" ) then
		PeW_Update();
		return;
	end

end

that should fix it