What size should I get to fit a girls size 12

I would go with a large. My daughter is 9 years old and she wears a size 8 and I bought her a medium. It fits her good maybe a little room for growth too. So I believe they run true to size. I would imagine a girl who is a 12 would be a large. They are awesome my daughter loves them

I think that would be a size 14

I am thinking the large was a 10. Medium 8 and small a 6. Just a guess.

What size is XL? I have 14 year old.

My daughter is a size 8 and I bought her a medium. Pending on how your daughter is built the XL will work. My daughter is tall and thin so there is still a little room to grow with the medium. If your daughter is more curvy the XL might be a little snug or no room for growth . Hope this helps. They are cute and my child loves them