What is the ruling on repentance and expiation for one who caused a diabetic girl to faint, which led to her pregnant mother's fright and miscarriage?

You must offer sincere repentance for what you have done. As for expiation and blood money, they are not obligatory upon you, because it does not appear that you were involved in the miscarriage, whether directly or as a cause. Liability is incumbent upon the direct perpetrator, or, if that is not possible, then upon the one who caused it.