Austria and some areas of Switzerland also have a form of Church Tax, which was institutionalised in Germany by Bismarck. Your writer's estimate of an average DM200-300 per month is exaggerated - DM80 would be nearer the mark. It applies to all denominations represented in Germany.
The Catholic church's authorities are very money-minded, even though they pay their clergy civil servant salary levels with all the accompanying perks. I don't blame Steffi for choosing to leave. Very few Germans would have felt anything other than a sympathetic understanding. If she chooses to move to Florida, or in fact anywhere apart from Switzerland or Austria, she will be free to go to church like any other Catholic.