Bitches will always put weight on after being Spayed. I would recommend you simply cut down the volume of food fed to your dog and get the exercise right.
Re; Chicken mince, yes it can be good stuff, but try and source good quality as some stuff I have seen looks like mushy soup once defrosted god know where it comes from. I use a Chicken & Tripe free flow mince from Prize Choice, it works out with my discount around £2.98 for 2kg and it good quality.
Thanks you mate top advice