Your question require more facts to answer. Depending on which visa you are talking about, either an H1B, J1, O, B, etc.
You need to find out what kind of visa she used to enter and what status was granted to her. Depending on the information, the duration of stay is determined. Therefore you need to get a copy of her I-94 and her visa and show it to an immigration lawyer who can answer your question. For more information about visas, click on the link below.
Note: The above is provided for informational purpose only, one should not act or refrain to act just on the information provided. No attorney-client relationship is created unless a retainer is signed.