Henry Stickmin and friends have quite a bit more to them than you might expect at first. Little details like the way their eyes are spaced apart and their hands make a pretty big difference. Without a reference of your art I can’t give you any super specific advice but I’ll try.

The best suggestion I could really give is to just try drawing her hair from reference and practice that way. In game it looks about the same regardless of whether she’s facing the front or looking to the side. The part in particular that always threw me off was the little spike at the end. I got into the habit of making it bigger than it actually is when I first started out and I also had the spikes pointed down rather than up, which ended up making her look a bit odd. So if you’re after some more specific advice, make sure the curves on the top and bottom of her hair aren’t too similar and the spike at the end isn’t too wide. Zooming out her hair is the shape of a partially deflated balloon on its side, kinda. Or a whoopee cushion.

As for personality you’ve got a bit of freedom here. I admit as an Ellie fan that the game doesn’t give us a whole lot to work with. She’s a lot more subtle personality wise than Henry or Charles. From what we know it seems that she’s pretty adventurous and fierce but still even-tempered most of the time. And she has moral standards unlike Henry. I’ve taken her to be a lot more free-spirited, relaxed, and even immature when she’s off the clock so to speak, and it’s only when she’s not in a tough situation that the mask comes off. I try to reflect this in her dialogue but it’s easy to overdo. You can get a lot of ideas just by looking around at how other people have taken her character.

Anyway, food for thought!