WELCOME!! Your new baby is extremely adorable! I am sorry for your recent loss - I'm sure you both miss her.
Chicken is fine for some (many, even), but just keep in mind that it is generally the most highly allergenic meat there is (to dogs) - so keep an eye on it. Your pup may have a sensitivity if given too much of it - so you could try both less per meal, as well as less times per week.
A very, very easily digested protein you could give is white fish (pollock, cod, sole, tilapia, whiting, trout etc) - you could toss that in w/ the kibble. Fish is super easy on their systems - so that may be an option if A.J. continues to have issues. Canned/mashed potatos are loved by most dogs - that would probably be a great treat for him too at meal times.
