The proponents of UBI often miss a few benefits of UBI. Your article is getting away from the usual discussion, which is good.
In your situation, a single Mom who can afford reduce her workweek from 50 to 40 hours indeed has a better life for her and her child. Another benefit is that those 10 “lost” hours are now being given to someone else. Maybe that someone needs the extra money more than the single mother.
In other words, the job market will open up for those looking for work.