Unbeknownst to me my elected's niece was seated on a jury. She was never asked if she was related to the district attorney. The DA is not involved in this case directly. Is that a problem?

Not now.

If it had been raised at voir dire, it likely would have resulted in her being struck, because that's a specific challenge for cause allowed by 35.16(c)(1) of the CCP. But it was forfeited when it wasn't raised.