You did a good thing, I would say, and it wasn't your fault you dreamt such dream which makes her leave her marriage; it was clearly a message to her through you so she wouldn't end her life miserably in the hands of someone who abused her.
At least you didn't keep this to yourself like the first one and you wouldn't want such thing to happen the second time.
This is why it's good to speak out on time before it's too late. You might not know how to confront the said person but there would be someone you can talk to to help relay such message to them.
Yea that's a good way to look at the situation, even though I wasn't happy it ended her marriage, seeing it saves her life and she has been happily married in her new marriage for the last four years or so makes me feel less guilty.