Why can't I receive my friend's text messages?

My friend and I text each other a lot. I have Verizon service and she has Sprint. As of Sunday afternoon though, I cannot receive any text messages from her and I know she has been sending them. I can get them from anyone else though. She can receive texts from me without any trouble though. I have updated my roaming capabilities, restarted my phone, made sure she has the right number, and made sure I didn't accidentally block her. I don't know what else to do. Sprint has told her that this is my problem. Does anyone know how to fix this?