Am I right in thinking that the sum of money involved is actually quite small, tens of thousands rather than hundreds of thousands?
Savings over £16,000 exclude you from UC, but savings of £6,000 are excluded.
I do not know the age or life expectancy of the OP but wouldn't the simplest thing be to gradually pass the money to her DD and spouse in small amounts as and when they need it,while she is alive until it is reducd to, say, £10,000 and then leave it to them as a cash sum. I assume that they have no saving at present. Their UC would be reduced, but not stopped until the amount fell to £6,000 and that would have them back on full UC with £6,000 safe in the bank.
How old is your DD or her husband. Are they near pension age? I ask because permitted capital limits there are higher, although I do not quite understand how this applies to the new style pensions.
You could put it in a trust to pay them the invested income and pass the capital over when your DD reaches pension age.
The problem is, that if the amount is small, the cost of setting up the trust will be £300 or more and then you need a trustee to administer the trust (not your DD or her DH), probably it will need to be a solicitor and that could cost another couple of hundred £ a year, so a lot of a relatively small some will be lost to ongoing legal fees.
I would say give them any money you can afford as and when needed while you live and leave them the lump sum when you die. The costs of running the trust over 5 or 10 year, if the amount is small, will probably exceed anything they would lose in UC if their savings went over the UC or pension limit.