Female cat keeps stealing Mommy kitties newborn kitten?

My female cat just had two kittens last night, sad to say that one died :( Anyways she has decided to keep the kitten under my bathroom sink, which isn't a big deal at all. Well, my other female cat keeps going under the sink and stealing the newborn kitten and trying to hide it in another part of my apartment. When I walk towards her she will place the kitten down and walk away and I will replace it back under the sink and mommy cat will quickly join to take care of her baby. I can't close my bathroom door because then my mother cat can't get out to eat and for a drink. Is there anything that I can possibly do to keep my other cat from kidnapping the baby? The cat that keeps stealing the cat had a litter about three months ago if that helps any. Thank you for taking the time to read and answer this.