are you breast feeding? Perfect excuse to go off to another room. If not, also I'd go with DD needing to feed in private as she's fussy...
If they start handing her around, walk up with a big smile on your face saying "oh, she doesn't like being passed about, best I take her back before she starts screaming the place down, I'm sure noone wants that!"
If people start giving you advice just keep saying "no, it's not XXX, it's just she doesn't like big groups of people, you're a bit of a shy one aren't you DD?" with a little smile and "I'll just take her in the other room to calm down, you all carry on."
Be firm, stand your ground, you are the mum now, keep telling yourself "I'm the alpha woman now, they can't boss me about" - they will try, but you just make it clear you are ignoring them and think they are wrong. Remember, they are being rude by trying to make out you don't know your own child, there's nothing wrong with making it clear that you think you know your baby better than they do.
Alternatively, when are you supposed to be going to PILs? I'd get strategic diarrhea....