There are three useful and reliable kinds of evidence in research in history. They are direct observation (as in interviews with participants in events), primary sources (as in diaries and letters etc) and secondary sources (as in what others say about primary sources like textbooks).
Discovery Channel's video "Secrets of Egypt’s Lost Queen" is reliable because it is a verbal report made by a representative of a team of researchers connected with the Museum of Cairo and with the University of Cairo who worked on primary sources (mummies and mummy paraphernalia) and discovered primary data. In addition, both institutions are themselves reliable sources of research and information. What researchers, or their representatives, associated with these institutions report can be counted on as reliable, objective and well mitigated (if there is room for doubt, results will be reported to reflect this doubt).
The video is also reliable because the research undertaken was not the theoretical kind but the empirical kind. Computer-Aided Detection (CAD) scans were used to "see" through mummy boxes, as Dr. Zahi Hawass describes them, to identify the contents and, in some cases, the identities behind those contents.
The CAD scans provided reliable and useful information about the ages of the mummies, the conditions of death and the relationship between stored body organs and the mummies in the boxes. As a result, a tooth could be traced to the mummy that it came from. Further, the mummy of Queen Hatshepsut could be identified and distinguished from her wet nurse (later, simply nurse as in Juliet's Nurse from Romeo and Juliet). It was also determined by CAD scan that the mummy with the "crying face" died at the moment that her face had this aspect.
This information is useful for obvious reasons. It allows identification of otherwise unidentified mummies, which is significantly useful since now it is known that Queen Hatsheput is in the Cairo Museum, rather than lost somewhere in the desert. It is also useful as it allows for furthering of analysis of ancient Egyptian history and allows for confirmation or overturning of theories of historical relevance. It is useful for other reasons in that it may give rise to new understandings and theories of the life and events in ancient Egypt.