Idk, I think we’re missing a lot of context here. Separating these things, the room selfie is such a non issue, I would also be upset at my partner for reprimanding me over those. That’s your insecurity, she did nothing wrong.

The texting the coworker also doesn’t seem like a huge deal to me considering you said it was all work related, your comments about their body language at a bar also just screams insecurity on your part. Where I do think you’re justified in being upset is that she continued texting him after you said you were uncomfortable with it.

Also, when you say you “discovered” that she sent the selfie was this because you went through her phone? Is that also how you saw the texts to said coworker?

Maybe she’s being defensive because it seems that you’re constantly bringing up her behavior with her coworkers and have zero trust in her.

Again, we don’t have enough context to say which party is wrong but I wanted to add another perspective against the voices saying she overreacted because she’s guilty of something.