1.As her technique develops, her self-confidence will develop CORRECT but using "develop" twice in 1 sentence is clumsy.
I would write: .As her technique develops, her self-confidence will increase.
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2.As her technique develops by, her self-confidence will develop.=INCORRECT
3.Her self-confidence will develop, along with her technique.=CORRECT
4.Her self-confidence will develop, with her technique.= clumsy. No 3 is better.