She is a small 5 y/o girl who seems very attracted to this world, I have not watched anime for a long time, at the time I saw little more than 300, but the ones I saw are not appropriate, anyway, I look for anime that do not have nothing related to ecchi, gore is not a problem, she already saw.
Demon Slayer Kimetsu no Yaiba
and
Grave of the Fireflies
But I don't know what to show and don't get bored.
Gakuen Babysitters, anime is literally centered around little children.
Wholesome, cute and fun. Everything you need in an anime to watch with a little sister.
School Babysitters
these ones are some really good anime i think fit in your criteria
The Disastrous Life of Saiki K
HINAMATSURI
Little Witch Academia TV (especially this one)
LaidBack Camp
LAIDBACK CAMP SEASON2
Can never go wrong recommending this one to children. Hell, it made me feel like a child at some points
Oreimo
great anime to watch with your sister and to bond with her
Saiki Kusuo no nan
Really funny, but the subtitles are SUPER fast.
Maoujou de Oyasumi
Hotarubi no Mori e
Noragami
If she enjoyed Demon Slayer, this might be fun.
Chuunibyou demo Koi ga Shitai
A very child friendly and cute romcom. I think it's great for younger people.
Cardcaptor Sakura
cute and fun
I highly recommend these
Little Witch Academia
Love Chunibyo Other Delusions
You could both give a try to the World Masterpiece Theater anime series. Their quality is really top level, they usually have interesting plots and characters, and they are targeted to children. They look a lot like Studio Ghibli (some staff who worked for Ghibli, including Miyazaki, also did WMT series) and you gain knowledge on literature as well. I'm currently watching these two and I'm loving them:
anilist.co/anime/2150
anilist.co/anime/2559
You would probably have to explain some stuff about the second one.
Otherwise I rec:
anilist.co/anime/99230
anilist.co/anime/530
anilist.co/anime/4081
4 years old is suuuper young, but in a few years I would also recommend:
anilist.co/anime/20754
anilist.co/anime/12883
anilist.co/anime/113415
anilist.co/anime/12531
anilist.co/anime/17909
anilist.co/anime/98436
These are different genres but I think they're all okay for children. Gakkou Gurashi and JJK have some gore, but it's framed in a very normal way (good characters injured = bad, sad, whereas evil character injured = we had to stop them so there was no choice). Of course, if you think she might be afraid or have nightmares, it's best to avoid those.
I feel like anything colorful would be pretty cool, so something like
Flip Flappers
very colorful and action packed, not goated, but pretty good, so you wont get bored.
Hyouka
Also very colorful and some interesting storytelling if you're into it.
KON
Just k-on, because more people need to watch it.
She's 4 years old and you're letting her watch serious anime like Grave of the Fireflies? Terrible choice. Let her be a child and let her see appropriate fun anime. I think Studio Ghibli movies are great for any age and a 4 year old would definitely like it. Perhaps watch Pokémon or Sailor Moon with her.