CCS is not for young kids. Yes, sure, the population is more of kids, but there are a lot of adults too. In fact, Sakura continues to be Japan's #1 most loved character. I understand that the whole plot, colors, and characters of CCS look like they're for young kids, but it's enjoyable for people of all ages, if they can just ignore the brightness and the cheerfulness. I think your friend is just frustrated with all the "kiddie" animes that are popping up and she just doesn't like CCS because of it and the whole fact that Sakura has to "capture" Clow Cards, like Ash capturing...uh...the "animals" in Pokemon. This is a main reason why, a lot of animes from Japan really don't make it over to the US. That's because a lot of people in the US like to watch a lot of action, gore, violence, etc. which is why cute animes like,
Kanon and
Tiny Snow Fairy Sugar never will make it over here. Fruits Basket is...surprisingly, going to be released in the US, and I'm sure it's going to flop, because everyone looks forward to action and all. But, if you take an anime, like Love Hina, with annoying characters and slap-stick annoying pranks, then it's all popular and good.
Personally, I feel that CCS is to be enjoyed by many people, despite their ages and that your friend just needs to....well....open her mind just a little.