Hill's KD and the RC NF are a larger kibble and the smallest bag I have seen is 8 lbs. Zipp, my older guy, is on a kidney diet and I have found it easier to do just the canned KD. I too have to play referee at breakfast and supper times as the other three "Z" like the KD. They sneak a bite at his food and he sneaks a few bites of their food.
I would ask some of your friends if they are feeding KD kibble and try a handful or two to see if Nikki can eat that size.
Zipp had no problem but he still has a full set of teeth at 16 yrs old.
Ask your vet if it is ok to feed Nikki other kibble for a few days if her kidney values are not bad but I would not try w/o asking first.
Feeding Frenzy

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Bob
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Zack, Zeke, Zoey, Zipp RIP 6/28/12