She may be overwhelmed with hormones and emotions since they have one month old twins and other kids. I think she should absolutely ask what is going on. Normally when anyone else is “talking to” someone in other posts, they are more than just texting them, it’s still spending time with someone else, even if it’s just a text. He is spending time outside an exhausted one month old twins! (Truly cannot imagine!) existence texting other women. Unless it’s shit about their shared kids, I can absolutely understand this reaction and I’m shocked she didn’t immediately ask him about it.
Even if it’s friendly, I can see the hormones making this unacceptable to many just-had-a-baby women. The hormones are unreal. At least they were for me and many I know.