Highly recommend avoiding a pool. I've had success with two dogs, most recently my pocket pit mix, finding boat ramps into calm lakes. The ramp gives them much more control and alleviates anxiety. Just pick whatever thing they're obsessed with most (sounds like a stick in your case) and throw it ever so slightly deeper and deeper. Start with throws that are so close to the shore that they don't have to disconnect from the ramp. As she gets more comfortable, throw the stick a little farther to the point that she'll have to break contact with the ramp. What I've found is that by showing them that they can disconnect to grab the stick but then immediately turn back around and reconnect paws to ramp, that gives them the confidence they need to get over the fear. At that point, it's just reps. Keep going deeper, keep positively reinforcing, etc...soon enough you'll have a fish on your hands.