The transfer on death indication is put on an account because the person wants those assets to become the other person's property. It is done to keep the assets out of probate, and the assets become the property of the person they are transferred to. Never, never, never put TOD on an account unless that is the person you want to own the assets. I am a stockbroker, and this notation is commonly put on accounts. People should not assume that they know the legal ramifications of such things as TOD, trusts, joint tenancies, etc. without proper research. Unfortunately, the 1/2 sister has done nothing illegal. The law has to assume that the person setting up the account that way was of sound judgement and his wishes were for her to have the money in the event of his death. That is what TOD means. I would strongly suggest that everybody look over your wills and the titles of all of your accounts, deeds, etc. I would also suggest that you do the same for any loved ones, especially if you think you may someday have an inheritance from them.
Examples:
TOD (transfer on death): the assets will transfer completely to the person listed without probate. It does not become part of the estate.
Joint Tenants WROS: The property is jointly owned. If one dies, the property transfers completely to the other person without probate. It does not become part of the estate.
Tenants In Common: Each person owns a portion of the property. When one person dies, their portion of the property becomes part of their estate and is passed to their heirs.
Be very careful when you open accounts or change registrations on accounts. It often doesn't matter what you put in your will if you register an account that lists a beneficial owner. Here is an example of a common problem. Somebody has children from a previous marriage and remarries. The children assume that since they are in the will they will get the assets. Meanwhile, Dad/Mom puts the new spouse on accounts or deeds as a joint tenant. When Dad/Mom passes away the kids don't get what they expected because it is now the property of the spouse-NO MATTER WHAT THE WILL SAID.