Call the jury commissioner at the phone number that should be listed on the summons or in the enclosed information. Explain the situation, especially the dementia, forget about the hip. The hip should get you a delay, the dementia should disqualify her. They will probably want a letter from her doctor saying that she has dementia, not just the issue about her hip. A jury is no place for someone suffering as your wife is. You and she have my sympathies.