Yeah you can mix it with another brand. That's exact what you would do when you switch her to any different food - even puppy to adult of the same brand.
Venus went from Fromm large breed puppy to adult gold when she was 7 months. The kibble is much larger than the puppy kibble - she might just be frustrated because it's more work to eat those tiny bits!
I mix in Fromm large breed adult sometimes. My dogs like the change up. The 4 star line is too rich for Otto, that's why we're on adult gold.
Love Fromm, Morgan was a fussy eater, she was 7 before I found Fromm. She went from not finishing her dinner all the time to no kibble left behind - although she'd throw a couple pieces to the cat. She had coarse fur too, Fromm 4 star duck and sweet potato made her fur very soft. Really popped up her colors too.
Venus of Crooked Creek 1/26/13
Otto von Hena-C 05/23/08
Morgan Donnermond 08/04/01 to 9/28/12 Long Live the Queen!
I have duct tape and I am not afraid to use it.