Thanks for the additional information Betty. I really appreciate it.
It absolutely sounds like you have the perfect example of a hunting dog on your hands.
Both Brittanys and Shorthairs, possibly more than any other breed, are infamous for their energy, hyperactivity and habit of getting themselves into trouble. It's possible that part of the problem lies in the fact that this dog doesn't get enough exercise (tired dogs don't get into as much trouble as others) and has been put on a harness (which can actually encourage these hunting breeds to pull more). Although it will be a great deal of work, this behavior CAN be changed.
The first thing you're going to need to do is get Cocoa on a strict regimen of exercise. I understand that you have already been walking her and taking her for regular walks, but hunting dogs NEED to be exercised every single day, and I'm talking more than a quick walk around the block. A high energy dog like this needs a couple miles a day to drain her energy and keep her from being too reactive things due to excess energy.
Additionally, she should be walked with a Gentle Leader (however, if this doesn't work, you may want to try a prong collar). I guarantee that she will eventually get used to it, and it will make her easier to control in the walking. The general rule of thumb is that if you control the head, you control the dog, so putting the leader on and leaving it on during the walk, regardless of how much of a temper tantrum she initially throws (and she absolutely will throw a temper tantrum in the beginning) is key. When she starts pawing at the Leader, simply give the leash a tug, say "Leave it!" and continue walking, even if it means you have to pull her along for a minute or so. Physics tells us that the dog can't paw at her face and walk at the same time...if you keep her moving forward, she'll have no choice but to leave the Gentle Leader alone and focus on walking.
In addition to the Gentle Leader on the walk (which should be several miles a day to burn some of that excess energy)..you may want to consider buying her a doggy backpack to wear. It can carry your keys, water bottle, treats for her. It gives her a job (carrying it) and the extra weight will wear her out on the walk faster than she would without it. Hunting dogs such as Spaniels and Shorthairs will often work harder if they're doing SOMETHING...so using the backpack may give her something to focus on other than trying to pull you all over the world.
Secondly, you might want to consider clicker training this dog. This involves buying a 'clicker' which has a little metal plate in it. You press the plate and the thing clicks, then you give the dog a treat immediately. Soon, the dog learns that the click brings a treat and will usually focus on you during the walk. http://www.clickertrainusa.com/clicker-training-videos.htm .
It absolutely sounds like you've got a great baseline for Cocoa, and I have no doubt that with a little tweaking, you can get this pulling under control.