This pro / non-pro discussion apparently tends to become a bit heated ;)
German track and field is based on club membership, and there is no formal distinction - or precise separation line in practice - between professionals and other athletes, nor is there any type of mandatory competition program. So things depend on what you define to be a pro.
Klosterhalfen finished school and started university studies in 2015, and in my view she is a professional athlete since winter 2015/2016.
Maybe we can agree that both Laura Muir and Konstanze Klosterhalfen have been successful in combining university studies with professional running.
Btw: I don't think that Sifan Hassan or anyone else will try the 1500 / 5000 double at the European Championships given that the finals are scheduled for 12th of August, 20:35 and 20:55 respectively.