Desperate for advice should my german shepherd dog need to be put down?

I horrible thing has happened my beloved german shepherd,has killed our old chihuahua he was 14yo just ripped him apart. Unfortunately not first time kill but most major. Has killed chickens and attacked other dog used to run with me while riding horse but now chancing horses and nipping at legs not stopping even... show more I horrible thing has happened my beloved german shepherd,has killed our old chihuahua he was 14yo just ripped him apart. Unfortunately not first time kill but most major. Has killed chickens and attacked other dog used to run with me while riding horse but now chancing horses and nipping at legs not stopping even when being called back. Has been trained by ex dog trainer never acted like this before, been aggressive since having litter but not towards humans. I love my girl to bits but seeing what she had done and troubles with her over a year span since killing all chickens in pen (6pox) parents wanting her to be put down is this reasonable? never had this before.Whats wrong with her? completely confused parents saying cause see is blooded?
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