My client had an injunction taken out against violent husband who has subsequently been imprisoned. Housing costs have been retricted as mortgage in excess of £100,00 and waiting time is the maximum 39 weeks. DWP say she was not abandoned because by taking out the injunction she consented to partner leaving.I understand their logic but is their any case law to the contrary? She is facing homelessness.

Don't know of any case law but can you not argue that he abandoned her by virtue of the conduct that caused her to seek an injunction? A sort of "constructive abandonment"?
You could also point out that not using such an interpretation could be sex discrimination: women are far more likely than men to need to seek injunctions against a violent partner, and thus get caught by this rule deeming them to have "consented" to the separation.