Wow that's a bit dramatic of her!! If I was her and was being given a family pet I would have checked, double checked and checked again just to be sure you were ok with giving away one of your babies (which it obviously is cos your husband is so distraught!) and even if you said you were sure I would still be waiting for the "I need my baby back" call
Yes it is going to be traumatic for her children but at the end of the day you have to do what makes you happy.
To delete you off Facebook before even seeing or speaking to you is just too funny! I just hope she doesnt punish the dog out of spite
At the end of the day, if she can't or doesn't want to understand why you are doing this and can't even be bothered to hear you out before reacting, do you really want here in your life?