Your 12 year old daughter will have to pay adult pricing at buffets, all you care to eat restaurants, dinner shows and dinner packages. The dining plan makes sense if you're planning on dining in those restaurants. Technically the kids menu is limited to kids under 10. Disney generally allows older kids, and even adults, to order from the kids menu but a few posters were charged an adult price.
Your daughter will have an adult plan, you could use her credits for two credit meals or for extra TS meals.