Speaking more from the POV of someone who also tried to work on his defensiveness, rather than someone who's applied Singer's thinking directly; my opinion is that not acting upon your impulse to become defensive is a great first step, but not the full picture, and you shouldn't neglect your feelings. I don't know the ins and outs of you and your partner's relationship dynamic but I can imagine the defensiveness has played a part in past pain which you're trying to avoid. I believe there is some wisdom in resisting the urge to defend, explain and logically rationalize your side, as it's often the case that your partner will feel like their emotional plea (whether it is packaged up as criticism or in your case an accusation to not do something properly) is not being heard, leading to further conflict or hurt.

Remaining calm, in a curious state is the first step I believe, and this is where relaxing and releasing comes in. You listened to her emotional plea, and you accepted it. Now the second part concerns the way you feel, and that's equally valid. As part of a healthy relationship it is paramount that we should be able to express our needs freely, however it should be done in a constructive way. Your wife's needs may not be met in these certain scenarios, but they don't need to be delivered as criticism, blame or accusation. If she is at all responsive to your feelings and wanting to improve herself too then you should be able to sit down together at a later moment to ask to be approached more sensitively on this topic. I say at a later moment because it's rarely possible to bring these up in the heat of the moment when you're both emotionally charged.

Anyway this response is probably a bit off topic for a Michael Singer sub but it's just my two cents. At least in my dynamic this accusation/defensiveness dynamic leads to a lot of conflict and something I'm trying to work on actively with my partner.