The dress is nice but the concert was at the church and the dress has too low cut for that. I understand that at weddings people seem to forget that church is a church and have a dress with a lot of cleavage showing. But other events at church are just that, events at church and people could show their respect to the church by dressing appropriately. I'm conservative at this, but people have different opinions of course. If the concert would have been at a concert hall, the dress would have been a good choice.
http://www3.pictures.zimbio.com/gi/Swedish+Royals+Attend+Christmas+Vasastan+Concert+MdHEkp9za_Kx.jpg
http://www.svenskdam.se/wp-content/uploads/2015/12/sofia-carl-philip-kyrka-ao.jpg
personally a low cut like this does not shock me to a concert in a church. This is not a religious meeting. Maybe this is a concert not to do it in a church in this case.