ee gads, I remember that book of Hanon exercises....

just wanted to second having her go along with you to pick out books - I was much more enthusiastic about my mom's books from 30 years earlier, than the brand new piano books I had when I was first learning. I took lessons for about, maybe 7-8 years.
Also wanted to send a big cheer for working with her yourself, heck even practice together, so it remains about having a fun, beautiful time together. I was so excited to learn when I was 6, we had an old piano and my mom had learned as a girl, but by the time I was seven and a first grader, I hated it. I learned, I played, but I clearly remember taking my reading workbook entitled "Seven is Magic" and writing in "n't" to reflect how I felt about my 7 pm piano practice time. Ugh. And that was only the second of 7-8 years of lessons.
Although I can still play most of Fur Elise from memory

My brother plays a lot on the piano, but he is 90% ear trained (he has a crazy ear for music) and he loves it - I'd also "hear hear!" the idea of helping her learn things she wants to play. He'd come home from high school and spend 3 hours teaching himself the piano part from "Don't Stop Believing," "Jump," "You're as cold as ice," etc. Can you tell it was the 80's...
Have fun together! I have this image of the great part in "Big" when Tom Hanks' character and his boss are playing music on the giant keyboard on the floor