[Given that she knows enough about the basic rules of the game, she can follow that well enough.]

I'm not going to waste time scolding you for murder because frankly, that's incredible, Forrest! You've come such a long way, I'm so proud of you! You really are making your mamma proud!

[She also gets where she's just never going to Get the murdergame premise and what it's like to be inside of one, so saying "murder is bad" just feels condescending. Forrest is a good boy who already knows that, and if he felt like murder was the only option, then it must have been really damn bad in there. So instead she'll focus on that part because she is so proud!! Her son killed a grown man with a mace!!!!]