I've been thinking about this for a while, and don't know if the OP is still around.
But now she declares that she hates the piano because she works hard on a piece, gets a sticker and then she's back to square 1 with the next piece and it never ends!
Well yeah! That's what learning the piano is all about. 
Tbh, I'd get bored too, and no, that is not what learning the piano is all about. It is not about reproducing one piece of music until it is good enough, then the next one, and the next one. That does seem rather pointless. Your reward for a good enough version is that you get to start all over again doing the same thing. It definitely is not what learning the piano is ALL about.
Learning the piano is about:
- understanding how notes work, understanding their language
- exploring the kinds of sounds you can produce: loud ones and quiet ones, connected and disconnected ones - and what kinds of feelings you can produce using this
- getting skills (see above)
- exploring harmony and disharmony, listening
This is an incomplete and probably inaccurate list. But these are the kinds of things that a good teacher would bring out.
y plan was to get her to what we call "preliminary" level and then there's lots of repertoire with CDs etc. I can buy so she can choose what she likes but first we have to get there!
The preliminary level is not about easy pieces. It is about skills and attitudes that the teacher sets up. By giving her this on your own, you may create a situation where a teacher has to undo a fair number of things.