URGENT HELP WITH EUTHANIZING MY DOG ?

About 7 months ago we found a stray dog on the side of the road and decided to take her in. She was an angel at first but then had numerous behavior problems we have managed to fix a few however she is dog agressive and is now human agressive she has never bit a human however we were always there to intervine when she was in her "attack" mode we have literally exhausted all options and the vet and staff at our vet feel that it is the best to euthnize her. We have called several local shelters and rescue groups however they are either all full or will not take an agressive dog. Out of the goodness of our hearts we took her in when no one else wanted her and now it has to come to this. It saddens me sooo deeply but the vet and everyone has told us there is nothing we could have done differntly and we did the BEST we possibly good. Should we put her down ???? HELP