Erika Steinbach's opinions wouldn't be out of step in the American right, but for Germany she is controversial for a reason - they're extremely out of step for the majority of the more left-leaning Europe. Opposing gay marriage is a very notable and rare position for a German political figure to take, and that's the reason it's being discussed.
Even though she is a prominent political figure, she is still only one opinion among many. One person's opinion about gay marriage, or any issue for that matter, does not reflect over an entire population of people. Granted, there are many who share her sentiments, but there are also those who don't. Moreover, there has even been conservatives in Germany that made statements in support of gay marriage.
I do not believe Erika Steinbach's opposition to gay marriage is supported by the majority of Germans. Erika Steinbach is an extremely conservative politician. Born in 1943, she strongly opposes abortion and gay marriage. I believe that her views may be those of many of the older generations. I believe that while many Germans may not condone gay marriage, there are a great many who support it.
The fact that there are still people who do not support gay marriage in a country does not mean everyone in that country feel the same way. I would think the majority of people in Germany would be for it. Many European countries accept gay marriage and give the same benefits even if it's just a union. Marriage is only a contract between two people anyway so one of these days people will understand that.
A majority of Germans probably supports gay marriage since same-sex unions are recognized by the European country. Civil unions have been recognized since 2001. Courts have generally supported benefits for same-sex couples while the main party in power has been against full marriage rights for homosexuals. I think a majority of Germans support gay marriage even though weddings aren't legal yet.