I haven’t had time to re-read the book (its been 40 years or so) but I did find this commentary in the guardian.
The quote in that article is slightly different: nine times out of ten, if a girl gets raped it’s partly her fault.
Though I would agree that the intent behind the quote is the same. I should point out that part the novel is framed as a series of ethical debates between the protagonist Jubal Harshaw and a variety of other characters, with the martian Valentine Michael Smith character as sort of a foil or counter example. An example of this is the disgust felt by one of Harshaw’s employees to the martian practice of cannibalism. This is rebutted by Harshaw.
I would have been more concerned if the sentence you quoted had come from Smith or Harshaw because they are put forward as the sources of truth in the book. But coming as it did from Jill, it could be viewed as a sort of foil for the views of those other characters.
Now having said that I could easily imagine these words coming from Dejah Thoris Burroughs in the Number of the Beast, so its fairly certain that Heinlein believed them at some level.
