Handling your preteen talking dirty

So we've always been open and honest with our kids. They've been raised with medical explanations of different body processes, including periods and sex. They've picked up other stuff from school and friends. My daughter is now 10, and has a 30B size already. She hasn't started her period yet, but she's got the once a month mood swing and cramping.

I give this background because here's the issue- I was changing the phone she shares with her brother to kids mode so the two year old could play with it. I found a string of dirty, explicit rp, with a stranger in an app chat room. While I tried to keep it calm, I know I was harsh. I don't want her to close up and not talk to me, but she's just too young for that level of explicitness. Advice?