I upgraded my kids iPhone 13 minis with iOS18 beta (public beta). RCS is used when we message each other individually which is great. I subsequently setup a group chat with my daugthers as the existing group chat would send messages with SMS only; once I setup that new chat between the three of us, both receive my messages as RCS. In this group chat, one daughter is sending messages with RCS and those messages are being received in the new RCS chat. However, the other daughter can send messages in the group chat only with SMS; those messages are being received in my original thread only. I checked and the messages app settings are the same for both. RCS is activated under settings --> apps --> messages and RCS works both ways with both of my daughters.
Any ideas how I can get my daughter to send messages with RCS instead of SMS in the group chat?