I don't feel like the letting her go speech had any affect whatsoever. Is it right to feel that?
It's like Pinhead said, she has heard so many speeches already that she has you tuned out. IMO, many H's won't give up expecting the WAW to "respond" to the long R talks or speeches, and she isn't going to do it. That is why you will need to start right now practicing to speak to her in one-three word sentences. For example: "Maybe....could be...don't know....we'll see....No....perhaps..." etc. Hold back the temptation of "explaining" your reasons, actions or plans.
Practice being the man you "need" to be--even if you don't "feel" the emotions right now. We all need an image of a better self--in whatever high standard we believe. Don't wait to feel the emotion of detachment....behave, act, pretend that you are. Have an attitude of "I could really care less what you do b/c I am focused on my life and my son". You don't tell her that....you just show the overt behavior as one who thinks it.
So....you need to brace yourself for the worse. Expect anything to happen. I suspect the first test will be you wanting to rescue her from whatever drama she produces. Time for her to put her big girl panties on and realize she's got to be responsible for her own poop and that you aren't cleaning it up any more!
If you truly let go of that rope, then she'll probably stumble and fall several times. Your job is to allow the circumstances that she has created...become the consequences she must endure. It's called "tough love".
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!