How can you get done by robbing your own home?

Ok hers the story. My sister in law and her hubby are going through a divorce and they both own their home so one day he tells her to go get some of the kids things from the house when he wasn't there. (she got her own key) then later that week the police turn up at her home where shes living at the moment with a warrant and search the bags she took with the kids things in because they said that she may be involved in a burglary ( how can they do this if she still half owns the house and has a key) plus they found a bag of white powder in the bags (that her hubby put there) hes stitched her up. how can she prove that hes done this :(