She didn't get her way. Of course she's upset! Was act so much like children it's uncanny.
You said "yes" and she tried to override you. That's not how this works. You have as much say as she does, and as long as that's not a standing household rule, you're good.
Just be aware that the further along you go on this ride, that the kids might start to see what they can get away with and with whom. They might ask mom and when she says "no" come back to you.
