Anonymous wrote:You can't control what your sister does. You can change how you react to it.
"Sis, we're not buying gifts this year. We're going to give to the food bank instead."
And if she buys gifts for you anyway, say thank you and move on.
I would not say "thank you" when someone violates a boundary you set and feeds their own addiction. Do you say "thank you" when your alcoholic cousin pulls out the wine? I would just calmly remind her you already said "no gifts" and give it back. Then move on. If she insists, you calmly keep the boundary.