Read this article, "Annie Proulx regrets writing Brokeback Mountain? She needs to let it go" and I agreed with the conclusion that she has to get it over herself.
Once a book is written, how it is being read or interpreted or being remembered, it is really up to the readers. It might not be the writer intend that it turned into a tragic romantic story between gay men, but that would be all the gay readers like to see it. So be it.
Who wouldn't want a nice ending, giving us the warm and cozy feeling that love wins in the end.
So, let it go and there is no regret getting all that cash from the book sales and movie deal.