Is it acceptable to put the blame on an instructor during an oral exam for a mistake?
That is an annoying thing that happened to you, and I can see why it would bother you.  University instructors are human, and we sometimes make mistakes, or misunderstand a question from a student, or have blind-spots in our knowledge.  It is certainly annoying to a student if this leads them to error.

However, there is a bigger issue here.  Setting aside the interpersonal issues of whether or not it is advisable to "blame the instructor", I would suggest you take a broader view of your responsibilities as a tertiary-level student.  By university level, it is expected that students are no longer children or adolescents, and they are old and ugly enough to critically assess what they are told by their teachers, and proceed on the basis of rational inquiry and evidence, rather than on the basis of faith-in-authority.  If you are told by an authority figure like a university instructor that X is true, then it is up to you as a student to seek evidence/argument to confirm this claim, and treat the claim with scepticism if there is not a clear and convincing explanation.

In your case, you were told something that was false by an instructor.  Since that thing was false, presumably your instructor could not have backed up the claim with a water-tight argument, had you inquired about the reasoning for the claim.  You say you "took her word for it", but that is not what tertiary-level instruction is about.  By taking her word for it you rejected the standard of reason and instead adopted the heuristic of believing that which is plausible, and is confirmed to you by the assertion of an authority figure.  You paid an appropriate price for that by getting caught in an error in your oral exam, so hopefully, lesson learned.

In this case your instructor probably just made a mistake when she asserted that error to you, or misunderstood your question.  However, in my view, it would even be legitimate as a teaching exercise if she intentionally gave you a wrong answer and then tested to see whether you would parrot it back to her in an oral exam.  The point here is this: you do not go to university to learn to uncritically repeat the assertions of authority figures with PhDs; you go to university to learn to reason rationally, based on evidence and logic.  You failed to do that in this case, so you made a mistake.  That is great, because university is where we go to make these mistakes, get penalised for them, and then learn not to do them again.