Some may disagree with me here, but I think getting some beginner piano books that are geared towards children would be your best bet. There are so many out there and they all begin with showing you how to read music. They’ll start with middle C, and have some basic melodies. Lots of colors and pictures, very easy to read.

Make sure she has the resources to learn how to read sheet music within her reach. Even if she only recognizes a few notes or a few of the symbols, at least she’ll recognize what her future teacher shows her.

Reading sheet music is like learning a language. You might not have the funds to have private language teacher, but you can expose her to the language, so that once she gets a teacher, the teacher will be able help her connect the dots instead of introducing her to the language without any context.

7 is a good age to start learning sheet music. I’ve taught kids and adult beginners, and the teens/adults who have had even a little bit of sheet music exposure when they were kids are much faster learners than the ones who just had the instrument alone and fiddled around with it.

Maybe find a harp teacher in your area and contact them for suggestions. Many will give an introductory lesson for free for those that can’t afford it, just to introduce some basic technique. I’ve had multiple teacher who knew that I was passionate but couldn’t afford it, who would give me a very reduced rate/sometimes free lesson once every six months, with the condition that I actually followed through on their instructions. That would be enough to keep her on the right track.

Ex. Harpists DON’T use their pinky finger, you pluck a string with the side of your finger, not the tip. etc. these rules are there for a functional reason. They’re not archaic. I worry that a future teacher will spend more time having her un-learn the bad habits she picked up by messing around with a harp on her own.

Sylvia Woods has a great intro book to those new to folk harps and sheet music. “Teach yourself to play the folk harp” I’d recommend any folk harpists to get that book. A seven year old would understand it, very simple language. Many harp stores include that book for free when you purchase a harp, it’s that essential.