Usually this would require a court order, although states vary.
If there was a durable power of attorney, continuing a pattern of gifting is usually permitted -- starting one is sometimes not unless authorized in the power or by court approval as it can involve horrible self-dealing by the attorney-in-fact.
The court here should be concerned about the money being spent down and the impact on the level of care for the person and possibly leaving the state the burden of caring for him, so a combination of evidence that there is more than enough money held in conservative investments, that there is a short life expectancy (medical opinion needed), and there would be an estate tax problem for his heirs and/or that this continues a pattern that hhe had created years ago and continued until his disability would usually suffice to have a judge authorize the conservator to make gifts.
