Roses and their Thorns

There's a French(?) fairy tale called Diamonds and Roses that's about a girl who, when ever she speaks, has diamonds and roses come out of her mouth. This happens because she was polite to a fairy disguised as a little old lady. Her sister, on the other hand, was rude to the fairy, and had snakes and toads come out of her mouth whenever she spoke.

I kind of combined the two ideas. Whenever this girl speaks the truth, roses come out of her mouth. When she lies, thorns.
I believe she's taken to writing.