MMS is ancient. Ancient enough that my carrier disabled it entirely. Maybe the flip phone UI is shitty, or the carrier hasn't supplied the necessary APN info to the phone, or the phone hasn't been set up to use that APN because of a bug, or they're using some kind of modernized, non-standard MMS media type or something, but there's no way that phone can't receive MMS at all.

Like I said in my other comment - She can't receive a message with a photo from me. Just text, she can. It's an old phone, I think a Kyocera, and I believe her carrier is Cricket Wireless.