I don't think you are asking too much. Sure we can be a little less tolerant of things when pg - but its no doubt been building anyway. I am the kind of person that would say "you're welcome" to them afterwards as a prompt. I do it to my own kids all the time when they forget to use their manners and thankfully with them its a genuine forgot and they apologise and say thank you.. but its no ruder than not being thanked in the first place.

But no - not being precious. I wouldnt just want someone barging into my house, helping themselves to whatever and completely ignoring that I exist. Thats pretty much what she is doing and it is outright rude!

ETA: IRL Situations - I am horrifically shy. I am the person in the corner who has about 3 chips because I am too shy to take anything more or eat a normal amount in front of people.... and yet I have never forgone my manners. Ever.