This is a good possible reason Apple doesn't include MMS.
Not all carriers and phones use/accept MMS the same way. There isn't a standard. The size of the photo more than likely is too big for the phone she has thus it won't display. Another phone on the same network may display it just fine. Just like when I owned one brand of phone and my wife another, she could send to me, but when I sent to her depending on the photo (where I got it...copied over from computer thus big, or camera from phone thus small as was cheap phone) she could only get the smaller pics.
Also when sending videos or sound, not all phones play all types....
In the end MMS is only good if you and all your friends have similar phones/brands. I cannot tell you how many times a various friend could not get a picture or video or tried to send one out and I couldn't get it.
Apple doesn't want to invest in something that
sometimes works. People would complain about it being the iPhone. I agree, why have it if there isn't a standard. Email and the protocols ARE a standard. And if the phone cannot read a file sent...at least you have it in email when you get home thus you don't just lose it to limbo like you would with MMS sometimes.
Come on people, think about your MMS past...you know it wasn't perfect. Also MMS was ONLY made up by carriers to GET MORE MONEY from you as MMS is not charged the same as SMS. Yes iPhone has unlimited data, but your friends don't most likely...you really want to be emailing 800x600 pictures to them and them being charged by the KB (note KILO, not MB).