Any business owner would have been able to deny service until just recently (the referendum, as you know, only passed last year). I think she was kind of asking for it when she was so cozy with the gay clients all along.
It appears to me the law about discrimination due to sexual orientation became effective in 1995. The gay marriage law became effective last year. So NO! they would not have been able to deny service without being taken to task. But now gay MARRIAGE brings a different problem. It is against her religious beliefs, just like it is against some religions beliefs to have to provide contraception.