Is it obligatory to inform the current husband about the sexual assault that occurred with the previous husband, and is this assault considered a sin on her part, and does it affect her health or childbirth?

Performing sodomy on a woman is a major sin. The wife did well by not obeying her husband, and there is no sin upon her if she was coerced. As for informing the second husband about what the first one used to do, it is not permissible, because it is an exposure of a Muslim's private matter, and no benefit is expected from it.