Absolutely. I would expect nothing else other than for her to refuse.
By the same token, then, if someone marched in and ordered a cake emblazoned with "F*ck Jesus" and the bakers said no, would that make them "Extreme religious bigots"? Or could they just be reasonable people who found it...
That's rather twisting facts to try and save your argument. All the major religions, whether worshipping God, Allah, Jesus, Mohammed, Shiva, Mithras or whoever have always defined marriage as a union between a man and a woman (or in some cases between a man and several women). All secular groups...