Responsible co-parenting or something else?

A single mom recently asked us an intriguing question.
Should she insist on meeting her ex-husband’s new girlfriend?
This all started when her tween daughter broke the news: “Daddy has a new girlfriend. We went swimming. And she wears a bikini with pink stripes. Her tattoo is so cool!  Next week we’re getting pedicures.”
While this single mom [...]