Is it permissible to educate a daughter in a co-educational school, which is the only one of good standard in the town, knowing that she will be prevented from interacting with boys and will be veiled upon reaching puberty, or is the alternative a school of Christian nuns?

A girl should not be taught in a mixed-gender school if other non-mixed schools are available, for the corruption of morals is a greater danger than a perceived decline in academic performance. If there are no girls-only schools, it is permissible to teach her in a mixed-gender school until she reaches an age where she becomes desirable, at which point she should be veiled from non-mahram men. Her education at the hands of nuns is a grave danger that must be avoided.