Hmm option b would be funny because no doubt she would presume you mean a woman...
In my sitch I just don't respond to anything that isn't daughter or financial related. Again a little different as I do have to speak to her daily when I/she ring our daughter. IM civil and friendly but don't get involved in any small talk. I ask nothing about her life. When she does sometimes try and chat I just cut the conversation. Not in a rude way, I just don't answer with responses that lead.
If you do want to say something then what about along the lines of " ex under the circumstances it isn't appropriate that there is contact between us unless it relates to the dogs" any divorce communication should go through your lawyer. No need to be nasty, no need to show emotion one way or another... Just straight to the point, business like.
Me:40 W:35 D:8 T:13 M:10 WAW: 7/14 PA Discovered: 1/15 at least 6 months Moved out and moved on