I would go with what she wants also.

If the fabrics truly go together, just remember that she chose them and she loves them...she made her first quilting decision...you don't want to squash her enthusiasm. you will be able to get the center assembled and then ask her to help choose the borders....she may see where that tiny flange border in a bright version of the pink just sets the whole thing off perfectly....or a pale lavendar in the right shade....whatever looks good....auditioning fabrics helps us to decide on the last touches...why not her? and THENNNNNN you will be able to show her a choice of different threads which is that last layer of color.... and then when she decides, whichever way it goes is her choice and you and she will know it is HER quilt.... she will love it and you will love knowing that she appreciates all your hard work...last ditch? put all her scraps and your color choices in a gorgeous back art that may show her what you were talking about without sabotaging her choice....

I would definitely work with only her choices. Just having a 13 year old girl involved in the process is a blessing.

Can you make two samples to show her the difference? Sometimes seeing is believing!

I would just go with what she picked. It will feel more like hers if you do...

I would not change her colors. I always heard that "beauty is in the eye of the beholder." I agree with others, she will always love it for so many reasons, and the fact that she picked out the fabrics will make it even more special. One day she may look at it and think "what was I thinking" but for now, it is beautiful for her. And it will be beautiful!

When I was a kid it was my way or the highway LOL! She has something in mind and a change would really ruin her plans. You won't have to look at it everyday so stick with her choices and in a few years you both can have a laugh over it, but I'm sure your effort will be well loved anyways.

Go with her choice. To suggest another colour will be saying you don't value her opinion. It might not be your taste but it's more important that you support her. It's just fabric and you may just find that she'll be willing and eager to participate in another project with you.

Be sure to wash and hot dry your flannel backing - it will shrink way more than the cotton in the top.

Totally agree with letting her choices stand. I had a girl that age tell me recently that the best thing about me was that I LISTENED to her. (I'm her piano teacher and let her make some choices about pieces to play.) Being heard is a huge thing at that age. (at any age actually!)