It's a very tricky area where matters of conscience are involved, but for me the crucial issue is that she asked to be allowed to abstain, rather than choosing to vote against gay couples seeking to adopt. She did not actively discriminate against people, the whole point was that she didn't want to be put in a situation where she would. Presumably, she could have said nothing and voted against it, claiming some spurious pretext.
We accept - generally - matters of conscience in other areas, the usual example being chemists with the morning after pill. In this case, it looks like she has been sacked for being honest and having an opinion, which isn't really fair. She merely asked to be relieved of being placed in a position where her conscience conflicted with her duties. Sacking her, rather than simply accepting her exemption, seems an extreme response.
The obvious counter argument would be that if the situation was changed, and she was refusing to perform her job because of racial or sexual prejudice, then it would be unacceptable. Quite. I did say, earlier on, that it was tricky. A line has to be drawn somewhere, and I certainly wouldn't approve of some vehement racist voting against something because of their bigotry. but she didn't do that, of course. She asked to be excused from voting.
A person should always be answerable to their conscience first.
Imagine the situation was reversed, and she was refusing to vote against a gay adoption because of her convictions. Then you'd be calling her a hero. You condemnation is predicated on her failure to conform to your perception of what is the right thing to do, just as you approval of her action in different circumstances would be based on her conforming to them, not a fundamental principle. It's shallow, expedient reasoning, that legitimizes as much terrible 'just doing me job' type behaviour as it condemns.
Ultimately, she lost her case, but this was probably because it was presented as an instance of religious discrimination. The tribunal ruled merely found there was no basis for a claim of religious discrimination. I think she's still got grounds for claiming unfair dismissal.
1 - "Christian advisor loses gay adoption case tribunal," unattributed report. Published by the BBC, 16th of Novemeber, 2010. (http://www.bbc.co.uk/news/uk-england-northamptonshire-11769358)