I am not childfree, but I saw this post on the forum and had to respond.
Only small people who feel badly about themselves feel the need to tear someone else down. They only tear down those whom they fear are above them. You will never be able to change a hateful person, but when I had to deal with a similiar situation I did the following, and it "got me through" the days.
1) I prayed constantly. For God to give me strength, for God to give her a less sharp tongue, for God to help me forgive her. (I actually began to pity her, so the prayers worked some.)
2) I recited the mantra in my mind, "Only small people need to tear others down to their depths," every time she said something vicious.
Of course, I didn't always handle it so well. There were times when a truly snide remark was made, and I would smile and say, "I don't know whether to compliment you for your ability to say whatever you think, or to chastize you for your rudeness."
It made her fume more, but it also shut her up.