Biography v. Historical Fiction

A script writer creating the dialogue for a film about the real war time experiences of a living person, recently described the difficulties she encountered when the real person looked at the script and repeatedly said, "I would never say that!" "I never did such a thing!"
This is surely the difficulty, too, in writing real characters into historical fiction. Is it alright to attribute thoughts and feelings to people, which they might never have thought or felt? In writing a factual biography, on the other hand, the writer - unless he/she is to come in for a load of criticism - is limited to expressing only what the primary sources show their subject to have thought, felt, said or done. How much allowance is made for the biographer to interpret the motives behind the subject's actions? Unless it comes 'straight from the horse's mouth' with a mountain of footnotes to support it, critics often object to a biographer expressing the subject's feelings without the cautionary 'perhaps', or 'maybe' which makes for very stilted reading.
Those authors who succeed in weaving authentic fiction - grounded in historically verifiable facts, with the added dimension of humanity, emotion and thought which is often lacking in biography - seem to me often to create a truer picture of real historical characters than can be found in factual biography. Sandra Worth's beautiful "Rose of York" trilogy, for example, brings the real Richard III alive again on the page in a way that a factual biography could never do.
Perhaps the writer of 'true' historical fiction has a harder -and far more exciting and rewarding - task - than a biographer, in that he or she must capture not only the events, reactions and interaction of the subject's life, but also capture the very essence of the person so that by the end of the book the reader feels he/she has truly become acquainted with a real person, and not just a two-dimensional character from history.