I don't have any disorders.....but I am probably worse than you when it comes to hair in my food and hair in my kitchen.
#1 - I keep extra hair bands for anyone that comes over to my house and I insist on long hair going up or back and I NEVER allow hair brushes and combs near my kitchen. It's out, out, out with those.
As far as dinner goes, this is your opportunity my dear to say something polite but firm. I would straight up ask her.....Who's hair is in the food? Does she keep her hair up while cooking? It is industry standard for all food prep personnel and chefs and line order cooks to wear hair nets. The least we can do at home is ensure that our own hair does not contaminate the family meal.
Use this dinner to observe her kitchen cleanliness and standards of preparing.
If I were you, I'd eat before going so you're not hungry during the meal and you can learn from the experience. Analyze your plate and look for an opportunity to ask her directly with "Oh my, there's a hair in here! Who's could it be?"
Maybe she's extremely far sighted? And can't see close up?
And don't feel bad about wasting the food. I've thrown out meals people have brought over....One girlfriend has waaaaay too many animals for my comfort...cats that walk around the counter tops.....is just too gross for my comfort. Shedding dogs and pooping birds...Nope, I pass on food from those types of homes.
Just remember it's the thought that counts and send a lovely thank you.
You might also bring a heavy Hors d'oeuvre (appetizer) and bottle of wine so your covered.