Once JW's get your daughter baptised, they could then influence her (bully her) to cut off association with you and demonize you further.
I would start by discussing with both children (age appropriate?) the seriousness of their baptism and the possible effects on your famlies relationship. Just reasoning with her personally that Jeus got baptised at an age around 30, might influence her. If Jesus got baptised at 30, and he certainly had his father's blessing that was evident by holy spirit desending in the form of a dove and his father voice from heaven, what is her hurry? Does she feel pressured by the father?
I'd be tempted to run it by a lawyer explaining the consequences of a minor's commitment in JW world. Baptism with JW's is not like any other religions infant baptism. With JW's baptism as a minor, your daughter will be expected immediately, at the age of 11, to bear the responsibility of an adult within the congregation. Depending on the country your in, there might be some motion that you could make in court that could delay it and/or contingent on a judges decision. At the least, a lawyer could write a "hammer" type letter to your husband, which would be better than writing a letter to the elders.