I think your six year old is probably right! The movies are a little intense. And they increase in intensity as Harry gets older. Since she hasn't seen any of them, I think it would be good to see them all before the new one!
The lady I talked to last night called tonight, she couldn't talk long, since she is leaving for a long weekend trip in the morning, but I thought it was really nice of her to call! I still have a hard time getting my head around it!