This is in fact a very common situation, and requires some VERY gentle handling.
There are many, many reasons why women lose interest in sex – some physical and some psychological – and for the most part, they can all be treated.
Hormonal changes, especially around menopause, can cause sex to become painful, and menopause too can produce some psychological symptoms that result in a lowered sex drive for women - often issues around self-image, and what is happening to her womanhood.
I would like you to have a look at the Mayo Clinic's take on this here. It is very informative and in plain language. Share this with your wife and see what she thinks.
She needs to understand quite clearly how this is making you feel - unloved, unwanted, rejected I suspect. This is something you both must talk about, but calmly and without blaming or shaming.
You do seem to have very clear ideas about what is ´normal´. Twice a week, you say. Now while that may be your normal, it may not be your wife’s normal. The fact is that if to try to apply rigid rules to this, you are going to fail, simply because sex to a timetable, or when somebody does not feel like it and feels forced into it, is very poor sex indeed. It also leads to a great deal of bitterness, and the other partner of feels abused. Strong words, I know, but sex is about feelings, not timetables. It may not be what you want to hear, but that is the fact.
However, bear in mind that this is a very difficult time for her, emotionally, physically and hormonally – so above all else, be gentle and don’t try to force things. Be kind and encouraging. Initiate sex gently and lovingly. Be romantic. Spoil her. You think she should dress up for you. Great. What sort of equivalent could you do for her? She will probably react well to that.
If you want to have a great relationship, you are going to have to focus more on her needs rather than yours, I’m afraid. I suspect that you would both benefit greatly from sensate focus therapy, which you should ask your therapist about. You’ll find the basic details of the approach here:
I do hope too that you are both involved in therapy, because this is not a one-sided issue.
Best wishes to you both,