"Talk to your lawyer" is always a good response. However, in this case she's not really trying to negotiate, she is looking for info. So I think it is ok to respond (by e-mail):
"In order to remove a name from the mortgage, it would have to be re-financed. As you know, we signed an agreement that we would not incur debt or sell off assets during the divorce process. Therefore, unfortunately, no action can be taken regarding the mortgage until the divorce is final. That is my understanding, at least, but I urge you to check with your lawyer."
In practice, any bank she went to would ask her marital status and whether a divorce was pending. They will not even consider a mortgage in that case.
I was thinking this would be a chance to be sympathetic about how difficult D is. But "talk to your lawyer" is always the safe answer.
On the other hand, if you want to really annoy your W, you can tell her that it would have been possible for you to refinance, right up to the minute she filed for divorce, but now your hands are tied.
