On this issue, I agree. If you run a B&B you have to recognise that it's a place of business that provides a service, and as such, laws that apply to businesses and serives apply to them.

‘Do not judge, so that you may not be judged. For with the judgement you make you will be judged, and the measure you give will be the measure you get. Why do you see the speck in your neighbour’s eye, but do not notice the log in your own eye? Or how can you say to your neighbour, “Let me take the speck out of your eye”, while the log is in your own eye? You hypocrite, first take the log out of your own eye, and then you will see clearly to take the speck out of your neighbour’s eye....

... ‘Not everyone who says to me, “Lord, Lord”, will enter the kingdom of heaven, but only one who does the will of my Father in heaven. On that day many will say to me, “Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many deeds of power in your name?” Then I will declare to them, “I never knew you; go away from me, you evildoers.”

I agree that the woman was wrong not serving them on the basis of their sexuality.

However the rule that you have to serve everyone that comes into your business is i think very very wrong.
I used to work nights in a fast food place, and due to high level of drunks and abusive people, was allowed to not serve people that presented a threat or were rude. We also closed the shop a couple times when people became too rude to control.
I think at the end of the day, it's the person's business, and if they don't want to serve customer they will close, end of it.