First of all, thank you SO MUCH for rescuing this dog and giving her a second chance!
I have never heard of Crown Royal dog food, do you mean Royal Canin? If so, it is not a great dog food, and pretty overpriced too. Look around at the reviews of four and five star reviews and choose a few brands. Study the brandās recall history to make sure they are not recently or frequently recalled. If they are not available locally, then you can order online, some sites that are popular are chewy.com pet flow.com. Stay away from doggiefood.com. It is best to have several brands and formulas to rotate between, if she can tolerate it, because no dog food is perfect. Make sure to transition really slowly, over at least a week, more if she needs it. You will want to feed more of the recommended amount suggested, 3-3.5% of her body weight, depending on how much weight she needs to gain.
I would recommend taking her to the vet soon, to make sure she does not have any health problems. The vet may have advice about weight gain as well.
I know it can be overwhelming and confusing to choose a dog food, feel free to ask any questions you might have. Good luck–and again, thanks for rescuing this dog!
