Owning any kind of bakery or restaurant is an incredibly hectic, fast-paced job, and the fact that this baker is so overcome with hatred for gay people that she wasted time on this foolishness is downright pathetic.
You're a baker. Bake cakes, sell cakes and shut the hell up. If you wanted to save humanity from sin, you should have joined the clergy.
Religion is too important to be left to the priests. That said, refusing to sell a cake saying "Happy Birthday <insert name here>!" because she was the woman's wife instead of her friend is definitely ridiculous.