Ho enjoy yourself! Have fun! If you don't have anything to say, just smile.
That's what I do at family get-togethers.
Just don't think that you have to be perfect, because no one is perfect and it will just cause you to get nervous. Be yourself and have a great time!
I personally don't really like get-togethers either, but I still survive and you will too.
So the lady has chickens, too? Take that as an advantage to start a good conversation! Tell her about BYC, ask her if she's ever heard of it..etc. Here are some good conversation starters for you, since she has chickens:
~"Have you ever hatched eggs in an incubator or with a broody hen? Were they from your chickens or from a hatchery?"
~"Where did you get your chickens?"
~"Have you ever heard of BackYardChickens.com?"
~"BackYardChickens is a great site! It's really easy to register and it's free. I go on their all the time; the community is great, too. I get lots of information about chickens there."
~"Is _________(her husband) interested in chickens, too?"
ETC......
Just be yourself and have fun!
Good luck!