Bathsheba is most famous for being the woman who committed adultery with David. Less famous is her ongoing influence in court, especially once David promised her that her son, Solomon, would be the next king.
She made few appearances in the official history, but she wasn’t a naive victim (well, not by the time Solomon grew up). She was about to become the Queen Mother, a powerful role in most courts.
She had enough influence for Nathan to ask her first: was Adonijah really to be the next king? What of Solomon?
It was a set-up, of course. Nathan sent her in to ask David first:
1 Kings 1:17-21My lord, you made a vow before the Lord your God when you said to me, ‘Your son Solomon will surely be the next king and will sit on my throne.’ But instead, Adonijah has made himself king, and my lord the king does not even know about it. He has sacrificed many cattle, fattened calves, and sheep, and he has invited all the king’s sons to attend the celebration. He also invited Abiathar the priest and Joab, the commander of the army. But he did not invite your servant Solomon. And now, my lord the king, all Israel is waiting for you to announce who will become king after you. If you do not act, my son Solomon and I will be treated as criminals as soon as my lord the king has died.”
Nathan approached the king as Bathsheba finished her piece and he asked a similar question, confirming in David’s mind that, yes, Adonijah really had tried to take the throne by bloodless coup.
Adonijah’s coup failed, Joab had backed the wrong man, and Bathsheba’s son became king.