I'm a bit take-no-prisoners on this stuff. My mum has developed her own tactic for dealing with this. She repeatedly forgets that I'm gay. She's old enough to be almost able to get away with it. Weirdly she then starts talking about when she worked in film and how she can recognise a homosexual at 60 paces. Or she runs out her new civil rights record and fiercely criticises our PM for banning gay marriage when it's, and I quote, 'an unfortunate accident of birth'.
You're entitled to be pissed off. More to the point, you're entitled to turn up with a fairly thunderous book or page of your own refuting her sentiments and insist she reads it.