It's your money and your choice. If you have an otherwise good relationship with your "thankless" niece, maybe it's because she is just "that way", so it may not be worth stewing over. If your relationship with her is not so good, that's another matter. In any case, be sure to limit the amounts of your current gifts to the maximum allowed by the IRS before the Federal gift tax kicks in. Last time I checked, you could give a maximum of $15,000 to an individual per year tax free. Any amount over that was taxed at 40%
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You don't say whether you have a formal estate plan, but it looks as if your estate is large enough that one may be in order. Go to a competent attorney who specializes in estate plans. You'll be surprised about the number of decisions you'll have to make, even for a straightforward even distribution of assets. An estate plan is not cheap, but it can save your heirs a lot of grief, and they will always think kindly of you for your thoughtfulness.

You don't say whether you have a formal estate plan, but it looks as if your estate is large enough that one may be in order. Go to a competent attorney who specializes in estate plans. You'll be surprised about the number of decisions you'll have to make, even for a straightforward even distribution of assets. An estate plan is not cheap, but it can save your heirs a lot of grief, and they will always think kindly of you for your thoughtfulness.