glenwoodswoman,
I tend to think that he stepdad did that on his own.
AS far as the WTBTS/GB is concerned, a Disfellowshipped person is DEAD in the eyes of Jehovah. I just don't think they would permit or endorse taking any kind of initiative towards someone who is DF'ed. A JW is not to associate with, have fellowship with, or even talk to a DF'ed person. However, if you are a family member, then they will allow a certain minimum amount of conversation, but it must be about the important "business at hand", but must not be anything to do with spiritual matters. A DF'ed person should imagine that the Battle of Armageddon has already taken place, and now the good little JW's are there in the New World. And where are you? In the grave, and out of existence. It's kind of like the prisoners who are on death row in the USA, and as they walk to their death chamber, the prison warden announces "Dead Man Walking." That, I think, is how a DF'ed person should see themselves in the eyes of all JW's.
Now, you have mentioned that you were disfellowshipped about 13 years ago, and that, at the time, your daughter disassociated herself (at age 15). The first question I have is, "Was she a baptized JW at the time?" If so, then I think it highly probable that she would have been disfellowshiped for apostasy. If she did not write a formal letter to the Elders about her disassociation, and was not formally disfellowshipped, they may have simply regarded your daughter as "inactive" as a result of your disfellowshipment. In other words, perhaps they did not consider your daughter responsible or apostate.
If that is the case, then perhaps your ex-husband does not feel like he is breaking any rules by writing to her, and so is now reaching out to her in a letter.
It is hard to assess this, when we don't know all the facts surrounding the case of your daughter.
Rod P.