That feeling of shame you've identified is interesting. It suggests that there is a dynamic in your family, or between you and your mother (and probably your other siblings) where you've been taught that your feeling of hurt (which is justified: who wants to be told their mother judges their appearance and thinks they're not pretty!) isn't an acceptable feeling. Shame both acknowledges your feeling of hurt and tells you that (other people) have found it 'wrong' and 'inappropriate'.
You can own that feeling. It's OK.
The other reason you might feel shame is because of another dynamic: it shows that you are hurt by your mother. Behind that might be all sorts of things. For example, perhaps there is a subtle dynamic of feeling that you are not entirely safe giving all your emotional well-being into the hands of your mother. So you are left with the technique of trying hard to care less.
You don't have to do that. You can accept that you would like care, and approval, and that it will hurt when/if you don't get that. But it is still OK to look elsewhere for intimate, nurturing care and to not look to your mother for that care.
I'm wondering if her 'box' thinking is actually a way of keeping you and your siblings at a distance. Who knows why? From this distance, it's all a guess.
It is difficult to confront these things with a parent head-on. Behind it might be a feeling that you are asking for 'care' and are worried that, in the confrontation - however kindly or thoughtfully done - the 'care' will be refused.
Anyway, that's all a guess - from a distance. Obviously, all you can do with it is read it, poke it around, see if any of it helps you in identifying things. You can use it to eliminate certain ideas, and maybe come to some ideas of your own.
Best of luck. 