Is your step dads sisters daughter any relation to you?

In most cases, your stepfather's wife is your mother.

If your stepfather is no longer married to your mother, and has married someone else, then that person is not related to you (unless you count "step-stepmother") and, assuming the marriage ended in divorce, he is now your ex-stepfather. However, if your stepfather is your legal guardian, or has adopted you, it may be convenient to consider his wife to be your stepmother.