Some happy endings are just not meant to be.

Oreo, the miracle dog who survived a six-story plunge after a heartless teen tossed her off a Brooklyn roof last summer, will have to be put to sleep because she’s too vicious to be adopted, officials said.

“Everything we’ve tried to do for her has not worked,” ASPCA President Ed Sayres said yesterday. “And she has gotten more aggressive.”

The ASPCA plans to euthanize her today.

The year-old pit-bull mix barely survived the July 18 fall from the roof of the Red Hook Houses, suffering two broken legs and fractured ribs. The ASPCA had hoped to find her a home.

But despite numerous attempts to train her, Oreo continues to lunge at and try to bite people and other dogs.

Fabian Henderson, 19, who threw her off the roof, will be sentenced on Dec. 1, He pleaded guilty to aggravated cruelty to animals.