I would tell her that you want to make her a quilt for Christmas and you would like to pick out the colors and the pattern with her. So she has a choice. You can show her a few patterns that you think she would like and let her choose the one she likes best. Also let her choose the color. All part of the gift. Then you make the quilt and gift her with it at Christmas. It will still be a surprise but she will have no idea exactly what the combination she choose will turn out to be..
I did that with my granddaughter when she was 10 and asked me to make her a quilt. We had a great time shopping for colors and looking at patterns. We did it online snuggled up on the sofa. I made the quilt, wrapped it up ( along with a matching pillowcase) and gave to her at Christmas. She was thrilled and uses it to this day to cuddle under. Even though she knew the color would be purple and the pattern was Wall Flowers by Missouri star. She is now 15 and it is still one of her prized gifts of all time.