While I have not done something like this myself, I do have an idea. You could set up an email address for her and have her friends text their messages to that email address. Then read the emails from that mailbox using your programming language's IMAP functions. Just be sure to display only those that come from a trusted source. You would have to make sure you only display messages that came from her friend's phone numbers. You can check out twitter too, though I'm not sure this would be possible with their API. Please let us know if you have any questions.
I hope the best for your relative.