When I examined the literature, the advice is to consult the GP; but for detailed information, and because the patient was in a hurry, I contacted the Regional Drug Information Unit in Newcastle to see exactly what the issue/problem is.
As usual and within a few minutes, I received an excellent response!
Basically, I was told that Miconazole is very poorly absorbed and so a small amount between the toes of a breastfeeding mother will lead to negligible absorption; and therefore there is only a very small risk indeed to the baby.
Armed with this information, the lady bought the product - and agreed to speak to the GP before using.
The Newcastle based Information Service is a really useful resource to use!