You're doing fine!!! Primal is a great pre=made. Just start off as they recommend, with one nugget in the morning and one in the evening. Watch body condition over the next week. If you need to adjust up or down, you can.
I like to feed at room temperature, but some dogs are fine straight out of the fridge. I just float a medallion in a ziplock baggy in a bowl of hot water. Then mash with a fork and feed.
During the transition to Primal, don't give in and feed any junk food (kibble or carb heavy treats). Let her body just get used to the new food. She'll probably be satisfied, as it's so nutrient dense and the fat/protein will keep her full.
You can sure try a do-it-yourself prey model raw later. For now, just get her transitioned onto the Primal. And relax! You are doing a great thing for her. Be confident in your choice.