IMessage and sms not going to one contact but receive from them

For the last few weeks my iMessage is not going through to one contact. They turn to sms. But she is not getting the sms text messages either. I can get her texts just fine. I’ve checked that she’s not blocked, have signed out and back into Imessaging, tried to send her a message through her contact info, changed my start new conversations from, powered off and back on my iPhone X. Nothing is working. I found lots of people asking about this and no solutions that were posted have worked and no new solutions have been posted in years. Any ideas from anyone in 2021?