I don't get it. Is it talking about bestiality or sodomy but is the woman the prisoner or someone else is prisoner?

Any help?

The married woman enjoyed having sex with a dog so she invited others to come watch.

My interpretation is that she was caught in the act by her neighbours. Or maybe it never happened and they just wanted her gone/imprisoned, who can say?

But the "evidence" in court is that the dog ran straight up to her, sealing her fate sadly.

So... She was the prisoner?

Yes