For harassment to be present in a case, it requires a pattern of unwanted contacts. Absent something very unusual, one successful contact would not constitute harassment.
Seems like there's more to this than has been revealed thus far. Btw I am not asking for further details; indeed, I don't want you posting anymore information on this subject. You describe the brother as "eventually" giving you a new email address, and then, out of the blue, you inquire whether it would be harassment for you to contact her through the new email address provided to you by her brother. On the surface your concern seems to make little sense. That's why I'm guessing there's a bit more to the story. In any event, you're the only one among us who knows the entire history. Unless you want to sit down with an attorney and recount that full story, you are going to have to make your own call on this one.
I agree with the other lawyers but if you have had a restraining order imposed in the past it is probably a no contact order and last for 3 years. Which means you can't e-mail her. At any rate if the relationship is over it's better not to return to something that appears to have been troubled.