I run a sight-singing course, but unfortunately don't live near Edinburgh
in my experience students learn to sight-sing with least pain if they take one small stage at a time. In the beginning I treat pitch and rhythm quite separately, and only combine them when the early steps are really confident.
Much depends on whether she already plays an instrument; if she does it will help.
I take it one step at a time, something like this:
1) Scale pattern (step-wise) exercises on equal notes (ie no rhythm to think about, just practise pitch, and get confident going up and down.)
2 Simple rhythm ex's on one note.
3) Combine scale patterns and simple rhythms (nothing complicated, maybe just crotchets and minims at first).
4) Memorise arpeggio pattern (doh me soh) and try exercises based on that ( 3 lines or 3 spaces on the stave, ) no rhythm at first.
5) Combine scale pattern with some arpeggio bits (eg doh me soh la soh fa me re doh) etc.
and so on. A really well-planned book is useful, with carefully graded exercises. You might find something at your local music shop, but make sure it's aimed at the right age-group.
Some church choirs have excellent training schemes in operation for youngsters, which include being taught to sight-sing. I wonder if that might be a possibility ?
I believe St Mary's episcopal has a good choir.
I hope these rough notes might give you a start. Ideally you would find someone local who could help person to person - let us know how you get on!
Maggie