Cant group text one person

[Tb94561]

ve a Samsung Edge7. I send out group texts to my friends but I have one particular friend that if she is in the group text, a message pops up that the message jas failed to send because that one person cannot be included in a group text. The other contacts can put her in a text and we all recieve it and we both can respond. I just cannot initiate the group text. She first had a Samsung, and now she jas switched to an iphone and we STILL have the problem. Leads me to believe its a setting in my phone. How do I fix it??