Since you are new to each other...a friendly "how it's going" session might be the way to do it.
Tell her the things she is doing well...and let her know what needs improving (texting)
It may have been perfectly OK with the person for whom she worked before...so in the interest of a good working relationship...give her a heads up before it gets to be a real problem.
Also, give her the opportunity to give you the same kind of feedback. (and the chance to prepare ahead of time)...you may be surprised at what she has to say about the things she is learning and what will help her do the job you want her to do.
I always found this kind of open communication to be important in my working relationships. It makes me want to work harder for my boss when i know that he/she is interested in my success and improvement too. Ultimately, if i do well, it makes the boss look good too!