Keep it simple. Presentation big, sleight small. I would recommend something avoiding straight mentalism as its more acting dependent and not everyone can pull it off, let alone a crowd full of layman. Here's a thought. Pull the birthday girl up, pander on about how birthday's are special. Not just because they are celebrations but because it's a anniversary of the moment we come into this world. As such, we are much more aligned with the universe. Our impact and abilities are heightened as we are vibrating in tune with the rest of the universe (or whatever patter you want to use) Tell her you are going to try an experiment to see just how in tune she is with the universe. hand out paper and pens to the rest of the group. Have her think select a card (FORCE THE CARD using your favorite method). Have her transmit that thought to everyone in the room silently. They write down the card that she is thinking of. EVERYONE gets it write. She truly is in tune and a psychic savant. Everyone cheers. (Just remember to key everyone in on what card it is. Make sure they wont forget. Everyone knows what happens and feels included and the attention is all on her and she feels amazing. Simple, straight forward. Only one sleight and it will play big. Good luck