If you've got access to any technical ponds - uniform depth - take the pup into the water with you and throw short retrieves so that she can go from a swimming start but won't have to go very far to get them. Keep moving around the pond making these short throws with as little excitement and as nonchalantly as possible.
Having seen this "mis-swim" in other pups (not mine), I'm inclined to believe the experienced people on this thread telling you to a) address it now and/or b) the pup may not come out of it.
MG