She is not overbred if that pic is indicative of what she usually looks like... as long as the drake isn't rough on her, they can mate many, many times a day and just the act of mating does not harm the duck... overbreeding issues are stress from a drake being rough, forcing the duck, tearing up her back and head from being rough... IF she showed those signs, yes, that stress *could* cause her additional issues... I do not see a single sign that she has any of that though...
And for the record, if any bird is depleting their bones of calcium to lay, then their system is not getting enough calcium or absorbing enough usable calcium to support their laying... depletion of bone calcium is dangerously unhealthy for them and can lead to additional problems in the future... just fyi...