Leeroy Jenkins
Footballguy
Maybe she took it and thats what made Tyrion a dwarf.I don't think there is anything really debunking the theory.
The World of Ice and Fire book tells us that Joanna was living at Casterly Rock when the twins were conceived, but Tywin was the Hand of the King at the time and living in Kings Landing. So, either he traveled home or she traveled to Kings Landing(where Aerys could've slept with her). So, while it makes it more unlikely, it still doesn't truly debunk it.
I personally don't think it was likely. We see so many mentions of moon's tea or some sort of abortificant in the story. Given the evidence that Joanna and Tywin truly loved each other I can't see her willingly sleeping with Aerys. So, if she were raped by him I would expect her to at least take an abortificant to ensure that she doesn't bear his children. I mean it could be possible, but it just seems unlikely to me.
 
	 
 
		 
 
		 
 
		 
 
		 
 
		 
   
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 It's like how it would have been if there had been Joffrey perspective chapters.
  It's like how it would have been if there had been Joffrey perspective chapters. 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		