We have two different types of shihan: organizational shihan (such as in the Birankai) and aikikai shihan. They may be different or they may be the same. The aikikai promotes to shihan and it seems the only ones in America that are shihan designated are 7th dan and above. Currently, there are no females I know of in the aikikai at 7th dan and since 1995 or 1997 (Seagal was one of the first) only a few males-more recently. Not true in Japan where many 6th dan are shihan as well. As to Japanese shihan there is one on staff at hombu to my knowledge, I believe this is the person although I may be wrong: Mariko Takamizo (I think Mariko is a female name but I could be wrong). I know the female shihan has done seminars outside of Japan in the past.
Dee Chen in the UK is a shihan with the Birankai, though it's not clear whether that is the same as being an Aikikai Shihan.
All current 'Birankai Shihan' ARE
Aikikai Shihans. Birankai itself is affiliated to Hombu Dojo and all Shihans hold Shihan certificates issued by Aikikai Hombu. This includes Dee Chen
Technically of course it is possible for Shihans from any Aikikai group, at a given time, to be awaiting official sanction from Hombu Dojo. However at this point in time all Birankai Shihans are fully ratified Aikikai Shihans. We at London Aikikai are of course very proud of the achievements of our Chief instructor, Dee Chen Shihan as well as those of the USA based Shihans Coryl Crane, Lorraine DiAnne, Elizabeth Lynn, Gloria E. Nomura, and Kristina Varjan.