Can my wife travel to Denmark (from UK) alone?

Hi

I am from Denmark, and my wife is from the US. We got married in Denmark around 3 years ago, and have live in the UK together for about 2½ years.

She has a UK Immigration Document that she got when we applied for visa. She has traveled to Denmark and back with me many times without any problem. Will she be able to travel to Denmark by herself to meet me while I am there? I am not worried about her travelling back to the UK, just her being able to get on a plane in the UK and get off it in Denmark.