Just as she agreed to "just do it", unless she was "truly" not in the mood and it was "unlikely" that said mood would improve, you must "just do it". "It", being of course, being cool with her saying "no." You will have to assume that, when she says "no" it is because she is "truly" not in the mood and that it is "unlikely" the mood will change. Don't go behind her words and quiz her about why she says no.
Sometimes it helps me to tell myself, "okay, babe...your loss." Sometimes it even helps to say it out loud to my W, with a wink and a grin. The attitude this broadcasts is "your vagina ain't gold-plated, and you just missed an opportunity to share our love with each other. Oh well, maybe you'll see the light next time."
(Now...don't go saying that last part out loud. Sheesh!)
I think it sounds like you and your W are on the road to a better relationship. Lucky you.
One caveat: If the "no"s start coming out ALL the time, then it's time to have a talk about it. As has been stated on here before, a woman has an absolute right to say "no" to sex...but a wife shouldn't say "no" each and every time. Still, even this discussion shouldn't occur in the heat of a rejection. It should occur when things are calmer.
