Jacky
I do appreciate your problems on the distance to reach a teacher but I think there are many parents (my own in the mid-1970s included) who drive hundreds of miles a week to get their children the right musical tuition. In my case, all those years ago, we went to London on a fortnighly basis for the level of tuition I needed then as a young oboist.
I really feel your daughter needs guidance now from an experienced musician/singing teacher to take her on. You don't say if you are a music teacher yourself or how she's acquired the musical skills she does have to date but I feel a student with talent (however young or old) needs guidance from others to learn and develop. I still go for training and lessons to keep myself in good order (and I'm a seasoned "pro" of many years standing) - we all need to learn and receive guidance, right through life.
An 11-year old who is keen needs to be stimulated and challenged by a good teacher and also needs guidance and training in technique and musicianship too. I really don't believe in such an expressive art form as music you can learn everything from CDs and books. An experienced teacher will also know how to develop/challenge your daughter musically without exams being the only route. Yes, of course, we all know of highly talented 11-year olds who are winning competitions and taking Grade 8 on their instruments but they are guided and taught. Also, the human voice is not like a piano or violin which can be replaced if it doesn't come up to scratch. Treat the human voice wrong at an early age and you may be saddled with the results for ever - you can't go to the music shop and buy a new one. Singing is a wonderfully healthy occupation to be encouraged in all but taking it really seriously needs guidance and patience!
Please consider taking on the mileage occasionally to find a teacher - as I said in my initial reply, if only for a consultation initially. There is so much to explore in music - your daughter needs that stimulation if she's going to flourish. After all, even the "greats" of the music world have had teachers to help them along the way. My encouragement would be to find one for your daughter now and let them take it from there.
Hope you are able to get something sorted but, whatever, all good wishes for your daughter's future success.