You posted a link a while ago, which I foolishly didn't save. It was for a software package to work on tracking problems costing £20. I've searched posts but can't find the one it was in, please can you post the link again?
It now appears that DD does have tracking problems. I delayed doing anything because a trip to the opticians threw up a focusing problem for which she is now, temporarily we hope, wearing glasses, and I wanted to see if they fixed her problems. They stopped her eyes hurting when she reads, but she is still doing a lot of the things that seem to indicate tracking problems, and it is impacting on her enjoyment of reading and preventing her picking up a book and reading just for fun. That's the main reason I feel I need to do something to at least try and improve things.
So, thanks in advance. :)