She also used her married name, “Mary Maxted”, on the credits of several of her early films.  So it wasn’t a name she hid, and in fact virtually every article on her either on the net or in print mentions her birth and married names, so I see no reason why Wikipedia should be denied this important info.  

Just to give two further examples here is her BFI page (which lists the birth/married names)
 http://ftvdb.bfi.org.uk/sift/individual/2982

And a fansite (ditto these two names)

http://afn33-marymillington.blogspot.com/