Prefacing by saying I'm not a tech. But, I'm hoping to be soon... taking the class at the end of this month.
Anyway, the Apex is a decent high weight seat for the price. However, it
requires that you have either adjustable headrests or high back seats in your car.
Your dd will need head support from the car's seats to at least the tops of her ears while she's in the Apex. It may not be a problem right now, but may become one as she gets taller. If you don't have high back seats, you'll probably have to look at other options if you want to get the most bang for your buck.
What's your
dd's torso height? Sit her against the wall and measure from the floor to her shoulders. I believe the Apex has 17" top slots... so her torso measurement will also give you an idea of how much room she'd have to grow in the seat.
It's also pretty big. My
dd is not quite as big as your
dd and she has a ton of growing room in it (we tried it at BRU)... it's actually almost too big for her. Also, you didn't say what kind of car you have, but that's also something to keep in mind... how it will fit.