Over this Christmas I am going to buy my SIL something expensive.
What is special about your SIL?
She is a thing that makes me happy to have in-laws
It's good to show appreciation to your family in law. This can strengthen family bonds between both families. This will make it easier for both families to get along.
True, I just don't want her falling on her face since she has no job and her husband is a loser.
While your reasons seem less kind now, it is still sweet that you want to show appreciation to your SIL. I think they'll love the expensive gift.