Hey, if Ellie wants to mother Gabbey, I say... let her! Put her in charge for a day or two. Once it's really her responsibility, maybe she won't want it so much anymore.
Once I had a problem with my six year old not wanting what was for dinner. Finally, one Sunday, I said, "Fine. You're in charge of the food for two days! That means, YOU can plan and fix the meals for yourself, me, and your brother."
I just wanted him to see that it wasn't the easiest thing in the world and not so nice when you plan and cook a meal for someone else at the table to turn their nose up!
At first, he cried a bit. I thought he was crying because he was in trouble, but when I asked him why he said, "I don't know what to make for dinner tomorrow!"
But, for two days, he planned meals and cooked a good bit of it. I helped with the hot stuff. He learned that it's not so easy.
I learned that he's old enough to help out more.
Perhaps Ellie needs more "family responsibility."
Glad the first day of school went well. A good teacher will make all the difference, too.