Weird Text Response

I sent a text to a friend who I have texted in the past, and who has texted me.  On her end, the message came "over from a phone number rather than your name" =  my phone #@mms.att.net. The format of her text was unconventional for a text as well  We both have iPhones; I don't know which version she has, but mine is older, 4s, but relatively recent OS.  I don't know her service provider either.  

I received texts from others at about the same time as this message, and there was nothing unusual about those back & forths at all.

Why this anomaly?  Is it an issue with her service or mine?