Hello Cathy Humphreys,
Thank you for reaching out in Apple Support Communities. We understand in a group iMessage, there's one user who can only send you a text message, but receives everyone's messages. We'll be happy to help.
We suggest to have that one user to verify that Group Messaging is toggled on. If the feature is already on, please have them turn it off and back on by going to Settings > Messages > Group Messaging.
If that doesn't help, we recommend to have that user leave the group text and you can re-invite them. Here's how: Leave a group text on your iPhone, iPad, or iPod touch and Add and remove people in group text messages
Please keep us posted with the results.
Kind regards.