Hi, thank you all for your responses. To answer a couple of questions, and a bit of an update.
To confirm DD's just turned 8.
Mam and daughter do plenty together - I'd not dream of getting in the way of them- DD can be very much mummy's girl (even though they rub each other up at times).
HoldMeCloser... - yes, I agree, to advance, a student obviously has to put in the effort and it is obvious when kids (and adults!) are just "going through the motions". Wrt "falling behind"- that doesn't really fit with what our (and I would wager most) dojo is about. Whilst students obviously look to their sempai (seniors) for inspiration and guidance (just as they look to set a positive example to their juniors), it is very much stressed that it's not a competition: belt advances are at a student's pace (obviously, occasionally kids, and adults especially, are sometimes pushed to challenge, but sensei doesn't set folk up to fail). There have been times I've been advised not to grade, times I've known I'm not ready, and also when I've been challenged (and subsequently passed), and I've let the little one know all this... Essentially, dad doesn't grade every time either.
This "not a competition" (I'm almost embarrassed to say) is what DW simply doesn't seem to get - she sees that other students may have advanced, and is "why them, and not our little one?".
So on to the update. DW's reaction to sensei (and me agreeing) to the little one missing this grading. On the drive home, we (DD and I) had a talk. I asked her how she felt about the grading, tried to be as open as possible, wanted her views, not coached views. She said she was a little upset, but understood. She asked me about missing gradings in the past and how I felt, so I answered honestly that yes, it's not great, but I just crack on and try again, because I love karate. By the time we got home, we were okay I thought.
Got home, and spoke to DW- I tried to explain the points I've put above, tried to keep it level and calm, but her reaction was not good. Again, the old lines come out- teacher has favourites, other people have graded etc. Every time I tried to express that karate is a personal journey, and I really feel it's about her own progression and fun, no one else's, I was talked (well, got to be almost shouted) down. I walked away, went to do tea for DD (DW is now "not hungry" - read toys out of the pram and pissed off with me).
I could hear my wife talking to DD from the kitchen- every question was leading, designed to get a response she wanted. Bloody furious- wanted to intervene, but then, you can't undermine the other parent's conversations, lest we end up having an argument in front of tyke.
So now I'm still pissed off - got nothing but monotone, monosyllabic responses after I put the little one to bed. Now I'm at work, left before anyone else was up. Fearing what she'll say to DD before school - like I'll come home tonight, and, fait acompli, tyke and I will no longer enjoy karate together. This was "our thing". Want to send a text asking her to not raise the subject of karate, to please take a back seat on this and promise her that if ever the little one doesn't want to go, I'll accept it without fuss. But then, I also feel that's appeasing the way she reacted last night, which I feel was unacceptable. This is obviously much more than just karate - it's how she speaks to me, which I've taken for ages, but really have to find a way to get her to moderate, to mellow: because whilst I can take it, I don't want DD to have to take it.