Hi pinkbrady,
my understanding of dietary management in renal disease (limited I have to say) is that while a low volume/% of protein is very important, what protein intake there is should be of high quality so TBH I am a little surprised that the diet recommended is
entirely protein free

Poor dog

Anyway,
HERE is a useful info site with several very good links from it which assist in dietary management and will hopefully provide details of the type of treats you're looking for or recipes on how to make some at home

Additionally it has a link to a support group which you (or your Gran if she has www access) may find beneficial at this time.
Very best wishes for this dear old girl - it must be very upsetting for your Gran.
HTH a little, Teri