Get already cut pieces of card stock - I've gotten these before and you can find them at almost any craft store (Hobby Lobby, Michael's). They come pre-cut to a great card size and come in a pack with multiple colors. You're going to use 2 pieces per card for this project. One needs to be slightly smaller on each side (you'll see this below), so you'll just need to cut it.
On the smaller of the 2 pieces, sew whatever you want with a regular thread and needle - like, the Christmas trees by my friend (sorry it's a bit blurry). I would assume tougher thread would be better. I was thinking it would be cool to sew words like "Thank You".
And the back... She just taped it to the back of the card stock.
Then glue (or use modpodge or even double sided tape) and stick it on the larger piece.
Thanks Danielle for this great gift and idea!!!