If your dog is gaining weight on a mere 150g per day of Burns,which is exceedingly low in fat and protein as it is then i would make an appointment with your vet.
How much exercise does she get daily,does she get plenty of outside(out of the garden) off lead walks?
150g seems like such a small amount,how does your dog handle it? Is she satisfied,does she pester you for more food etc etc?
>Burns do a diet food think it's called high oats if you wanted to try her on that.
>Or there are other low fat completes that you could try her on.<
I think burns is quite low in enough in fat,with changing to high oats version which is even lower in fat,and higher in grain

I have seen and heard time and again dogs putting ON weight with low fat foods due to their high grain/carb content,or not losing weight at all.These diets seem to be designed to maintain weight so the dog doesnt put on anymore,and IMHO should not be fed longterm as they are filled with mostly fillers that the dogs cant digest and just poop straight out.They have 'just' enough minerals,fat,protein etc to meet the minimum of standards,and i really worry about the dogs who are put on these food for a short amount of time,never mind long term