My WW says some things that are really challenging to validate too; here are some of the responses I've used (mostly cribbed from various sources):
"I hear you." "That must be so frustrating." "I hear what you're saying. It's tough for me to hear, and I'm not sure how to respond, but I do hear you." "That is an interesting perspective." "I can see that you are really upset."
As I recall the DR book had a little example about a person who actually used showing a little anger as a 180... kinda giving the wife a 2x4/truth dart. I've been very tempted to do that with some of the things my WW has said, but it seems so anathema to DBing that I haven't risked it.
Me, WW - Upper 30s BD - Apr 1 2016 EA - Apr 7 2016 (discovered; ongoing for months; did not confront right away) Confronted wife about EA - May 17 Wife sent NC email to OM - July 11