8 years old is young for hand coordination if she hasn't sewn before. Simple is good.
Sewing a one piece blanket out of fleece with pinked edges is a simple place to start. She could applique hearts or other simple shapes onto it.
Another simple project my mom did with her granddaughters when they started was makiing Barbie sleeping bags. That can be really simple and might be something their Barbie doesn't already have. They were really more like envelopes or large scissors holders -- open on one end and part way down the side; certainly no zipper.
Be prepared for a possible short attention span calling for breaks in the sewing session.
Whatever project you choose, you and she will both have fun and be making memories!
Dayle
Dayle