I can imagine how torn you are about this... Try not to worry and enjoy each and every moment while you are away with your DH and beloved lab. Your mother will most likely be okay for the weekend. There are so many things we have no control over.
Deep down your mother would not want to keep you away from a break with your DH. You know she will be well taken care of. Go - enjoy! Let your dear mother know how much you love her before you go. That is all we can ever really do anyway...
Love and Hugs from Glenda