Older dog not eating food until puppy has finished her food.

[Xena Rio's Mum]

As some of you know on here I have two Rotties, one 8yr old Rio and one 22 week old Kya. My question is that Rio will not eat her food until Kya has finished hers, the only conclusion I can come to is that in the past Xena was the dominant one out of the two of them and Rio has just carried on being the submissive one. I have tried not feeding Kya and put Rio's food down on her own but she still does the same and leaves it until we have fed Kya. It is not a problem to me as neither of them are agressive over food and can be fed side by side, it just seems a little odd that the older one doesn't want to eat before the pup. Has anyone else had this happen to them?