How can I stop my child from reaching stuff above her head?

Move stuff farther. Children are naturally curious, so it is not possible to stop them from trying to reach for stuff above their heads. Therefore, the parents must move the stuff up so high that the kids won't even bother trying to reach the stuff. Also, remove any means by which the kids could climb up (climbing can be dangerous when a child falls).
You can't. It's gonna be easier to child proof your home than prevent your baby from reaching up over her head to grab something "fun". Move sharp or breakable items to the highest shelves. Make sure you use the back burners on your stove and turn all pot handles inward so your daughter can't pull hot liquid on top of herself. Never leave coffee mugs at a reachable height - those are notoriously dangerous.
Out of sight. Out of sight , out of mind! seriously though some toddlers are climbers and explorers. Get used to the fact that they need to be supervised at all times! (know where they are and what they are doing.) this is why parents are whooped by their child's bedtime!