Doubt it. Her mom is very computer illiterate. And that's very true. This is obviously a security risk relating to AT&T. This definitely should not be happening.
Have you tried calling ATT?
When I called, I was told there's no problem on their end, even though they were able to confirm my wife sent me 3 MMS messages that were showing up as being sent from a different number on my phone. Hm, ATT doesn't think that's their problem?
You might be told the same, but regardless, I think the more they hear from us the better (hopefully).