At only five months, she's not "ruined". Most likely the cute puppy behavior is just no longer so cute. She is also entering her "teenage" stage where she may not listen and challenge your authority.
I would suggest you try the Nothing in Life is Free program on her. There is lots of information about it on the internet, but here are a few links.
Nothing in Life is Free Dogs: Positive Reinforcement Training : The Humane Society of the United States