Well, my friend has official sources for other quotes, she has a scientific background and wants to make everything look perfect. A dispute about a 'quote culture' is unneccessary.
There are many examples for quotes that were misattributed. For example. Stalin's best-known cynical words:
"The death of one man is a tragedy, the death of millions is a statistic."
Unfortunately for millions of human beings he walked the talk he never said. There is absolutely no proof that he ever said that.
Same dictator, other example:
Death solves all problems — no man, no problem.
This actually comes from the novel Children of the Arbat (1987) by Anatoly Rybakov. In his later book The Novel of Memories (In Russian) Rybakov has admitted that he made the quotation up.
(And to be exact, these examples were stolen by me, from Wikipedia.