I think a lot of people are missing the OP's point.
If the OP isn't named in the will, then any deed of variation that might arise is no more her problem than it is my dog's problem if I had a dog. Therefore the "accidental" part doesn't cut it, because why is her name linked to the estate in question in order for the "accident" to occur?
If the OP is named in the will, then a deed of variation may or may not require her signature (it requires the signature of everyone affected, not all beneficiaries) but it's a little odd that it should have been sent out if a DoV were not, in fact, being drawn up?
The business about the tax code is particularly odd. You don't pay income tax on inheritances, but you do pay income tax on distributed income from invested inheritances; if someone puts money in trust with the income payable to you, that money is taxable as income.
But if you're 41, you can dissolve such trusts; executors cannot, for example, put money left to an adult beneficiary into a trust over the head of the beneficiary - the classic "oh, they'll spend it all" - whether the deceased wants it or not, because the beneficiary can simply have the trust dissolved (this is not legal advice, reality is more complex, there are exceptions, etc etc).
So the whole thing is most odd. Over on MSE's fascinating death and probate board, there's a bizarre story of an elderly executor who has completely misinterpreted a will that asks her to sell property and distribute the proceeds as sell property and keep the proceeds, and much fun is ensuing.
OP, the power of attorney is irrelevant: it ceases with death. You need to investigate what's going on because it all sounds very, very odd. Who is the executor, by the way, your mother or the bank?