I don't have personal experience with Harrington's Turkey and Rice flavour, but from what you've described, I can offer some thoughts.
If the Turkey and Rice flavour is part of their puppy line, you might want to consider switching to an adult food by now. I usually recommend making this switch around 4-6 months of age.
As for the bright colour of the stools, it's likely related to the food itself. I tend to prefer to see a darker colour in the stool, which you would certainly achieve with a different food. This forum has a strong presence of members that promote Raw diets. There are a few on here from the UK, who will hopefully chime in
The soft consistency of the stools could be a sign that you're feeding her a bit too much. According to Harrington's website, the recommended portion for a dog of her size is around "150-250g between 3 meals per day." It looks like you might be feeding her twice as much as recommended, and that could be why the stools are soft.
You want the fecal consistency to be firm, kind of like slightly dried playdough. This change in the amount of food might help you get to that consistency.