2.5" x 3.5" Soft Trading Card Penny Sleeves (1000ct)

Here are some things that can help to start. Cameo card list. It's a cheaper way to round out collections with favorite Pokémon. https://www.reddit.com/r/PokemonTCG/s/YFyJkIZWPX Here is a cheap but sturdy binder in different colors. https://a.co/d/0b2vXiK8 For sleeves you can you go regular size sleeves https://a.co/d/0fxjU4Cp Or perfect fit/ inner sleeves. Which is going to perfectly fit around the edges of the Pokemon card. Which makes it less likely to slip out. But it's also a bit more awkward to push in if you're not careful with it (People will use both sizes together) https://a.co/d/05RYKG20 If she likes carrying a single card around you can use top loaders with the sleeves (never put a card in raw in a top loader. Also some top loaders can be pointy on top so also check before handing one to her) https://a.co/d/01pJEFBE And then a team bag to make sure it doesn't slip out (she's so little I imagine she'll probably be excited and jumping/running around lol) https://a.co/d/01BNkDjb There are a ton of different options of everything I've listed. So don't be afraid to look around for a price you like better or a color she likes better (I would stay away from O ring binders as it's really easy to have user error and dent the cards). Just make sure anything that's physically touching the card is PVC free as that type of plastic degrades over time and can ruin a card. Hope this helps even a little!