Unfortunately there is no real answer to your question

There are lots of great foods out there and each dog does differently on them.
Lots of dogs do well on TOTW but yes, it is manufactured by Diamond which is a company that does not have the greatest track record. It comes down to what you're comfortable with - personally I am not comfortable feeding any Diamond products, but some people are if the dog does well on it.
Some food brands I like...
Fromm
Orijen
Acana
Pure Vita
Canine Caviar
Natures Logic
I tend to like gentle/natural shampoos ie, Earthbath, Buddy Wash, or Mutt Nose Best. I've used all 3 brands with great success - they smell good and leave my dogs soft and shiny.
The dry skin may or may not be caused by her diet. It's not uncommon during the colder months of the year for their skin to take a bit of a beating - Juno's been battling flaky skin all winter. It's helpful to use a gentle shampoo so you don't dry out the skin further, and make sure to rinse rinse rinse thoroughly. Adding a conditioner can help moisturize too.