It gripes me to no end. I've watched these situations my entire life. One child cares for the ailing parent with no help from the other siblings, and often while receiving criticism from the others about whatever perceived injustice they can dream up. It boils down to this - The caregiver is always the goat. I've seen it in all walks of life. Two preachers - in both cases, the whole family is ticked off at the one sister who took her dad into her home and cared for him. A deacon friend - the whole family is ticked off at a brother who took their dad into his home and cared for him. And several more. In ALL cases, the gripers expected dad to move into their sibling's home with "X" dollars, live there for an extended period, with 24 hour care, while his health declined to his eventual death, and upon his death still have "X" dollars in his bank account to be divided equally among all of the children. These greedy jealous animals totally discount any idea of the high cost of medicines, doctor visits, special facilities needed to accommodate the elderly etc. And that doesn't even touch the disruption wrought to the caregivers family. I know there are exceptions, but they seem to be rare.
I have given orders to my kids to NOT take me into their home when my health declines. Sometimes the family comes out intact, many times it is destroyed. In the case of the two preachers, ten years have gone by and one won't speak to his sister or any member of sis's family. The other is barely civil - a "frosted" relationship, you might say. Jealousy and greed. The caregiver is the goat. Your wife's ex-sister in law needs to accept that and write these people off for what they are.