Wow. Sorry, I forgot some people are still paying separately for individual features. I don't know why, since there are several wireless companies now that bundle it all (talk/txt/long distance/wifi) into a single package for a flat monthly rate. Jeez, I just threw away a ten-dollar Trac phone a few months ago and even it had texting. Well, I guess if you send the message and don't get a reply within an hour or so, you'll know.
You could just call her and read the same message out loud, verbatim, it works either way. Might want to add a "hi" at the beginning, or insert a "I'm sorry to bother you, but" right after [her name]. Chances are, she'll just hand the phone to your friend, and your social anxieties will be over. Don't sweat it so much, unless she's very strange I doubt she'll be judging you. She could turn out to be a very nice cougary MILF.
I'm just kidding. Hope that didn't make you even more nervous about calling.
Good luck.