I don't have kids and I'm only marginally proficient at taking care of my own head, but I remember some of the stuff my mom used to do to me when I was little. For one thing, don't brush her hair, comb it through with a wide tooth comb while it's wet and has conditioner in and detangle from the bottom up. Learned that one the hard way - to this day I just don't feel pain if you tug on my hair hard.
She also used FSG and had the recipe down pat - 5 tablespoons for half a liter of water (roughly two cups) and simmer for 20 minutes. Now with all the additions you can put in there that may vary, but that's how she used to make it for me.
She used to use conditioner as my leave-in too and was not shy about using that. She would add a couple drops of baby oil to a whole bottle for that purpose. There are a lot more oils to be used now that probably are better than baby oil, but yeah.
As for hairstyles, oh my god she is at that cute age when they can wear all types of headbands and tiaras and pins and things. And there are soooo many of these things right now. Take advantage of that!
Also, learn to french-braid! Mom used to part my hair in the middle and french braid both halves close to the head on both sides and join them at the back. It's good for a more controlled look, it's cute and when you take it out her hair will be awesome.
Hope that helped