First of all, the term Rav Moshe used is “Cholov companies”.
If she can read Hebrew, get her a copy of the Shulchan Aruch (Y”D 115) and the Teshuvos of the Iggros Moshe (Y”D section 1, pages 82-89). They can be found at http://www.hebrewbooks.org
Here’s some informative articles:
http://www.oukosher.org/index.php/common/article/chalav_yisroel/
http://www.oukosher.org/index.php/articles/single_print/5688
The more she knows, the more comfortable she will feel.