Individual text messages are delivered but group messages aren’t

My mother switched cell carriers recently, and around that time started not being able to receive texts that I send her as group texts to the whole family. We all are on apple devices. Around that time I noticed that my messages in the group text started being green whereas earlier (further up the text thread) they are blue. What is strange is that if I send her non group texts those go through and are blue.

There was a time during her carrier switch when she temporarily had a new phone number before porting her old number to the new carrier. I suspect the group texts are somehow bonded to that temp number, but don’t know how to unbind. I have removed the temp number from her contact in my iPhone 11 contacts. I have tried deleting the group text and starting a new one by manually entering the family members, but that still has the issue where texts are not delivered to mom, and appear green.

How to fix so group texts are blue and go through to her?