Mr. Berman is correct ... she needs documents from her home ... proving that she has strong 'ties' that will make her return home at the end of her SHORT visit in the US.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
Also, if there is an important event which is the reason she is coming, i.e. wedding, graduation etc. you can do an invitation letter indicating the reason she is coming to try to prove her non-immigrant intent.