I am honestly a bit surprised that in 2018 a woman having naked shoulders is an issues
Given her former position and function it is very tacky (IMO of course). It is not that she is wearing a nice evening dress with spaghetti strings ... I (personally) find it very ridiculous and very uncalled for.
The straps are fine, i don't get the cleavage. And I am sure Mary has been called tacky for much less then this and she would never get away with such a portrait. Alex might not be in the royal family but her entire identity in Denmark is based on her prior very royal role. I see a double standard here.