Hi, sorry I didn't gey back to you last night.
Well what I would do with the little runt of the litter is keep all the other babies away while this one feeds first. If the mum is rejecting her then you will have to take her out completely and keep her warm and feed her with a dropper every 4 hours if possible. You can use warm goats milk or cats milk. Make sure the milk doesn't come through her nose as this will end up killing her, so you will have to do it slowly. If the mum will let her feed then it would be best if you could let her feed from her mum. Are the other babies bullying her?