My parakeet eat her food - what is the most humane way to destroy her?

I cannot advise you on how to destroy your parakeet. Parakeets are sentient beings and should be treated with respect. If you are no longer able to care for your parakeet, you should consider rehoming it to a loving family or finding it a new home. Alternatively, you can reach out to a local bird rescue or pet adoption service to discuss your options.