Book recommendations please - Is Harry Potter suitable for a 6yo?

[IAmATriangleIAmAShape]

My 6 yo is an amazing reader, she picked it up age 3 and now reads at an adult level (lord knows why) but I'm struggling to find books that are appropriate for her and are challenging enough.

I've never read the Harry Potter books (or seen the films) are these OK for a (not particularly sensitive) 6yo?.

Any other recommendations please. She loves all things fantasy, dragons, angels, fairies etc, but will read just about anything, I would love any recommendations for some books with strong female characters as well please. I'm not much of a reader so I'm struggling.

The books get longer and darker after the first three. I think a 6 year old could cope with the first couple, if they are advanced for their age. The third book has a few time shift narratives that I’m not sure they could cope with.

I would wait. She will get more out of them once she's older even if the first couple are technically fine.

Has she read How to train your dragon? Or the Mr Gumm series (has a great little girl character in them). Or I'd look at Beast Quest just because if she likes them there are LOADS.