15week old Siamese won't stop crying and my part Siamese kitten seems to hate her

Hi I have a 21 week old Siamese cross kitten who needed a friend to play with when ever I'm not around. I just bought a 15 week old Siamese kitten who is tiny and won't stop crying all day and night. She is eating fine but never stops crying for more than a few seconds. Also my Siamese cross does not like her. She hisses and growls at the younger kitten and pounces next to her to scare her. We keep them separate when we are not around but there is a glass door separating them so they can see each other. I keep exchanging blankets so they get used to each others smells. I'm sure they will be friends soon but it's the meowing that's hard to deal with. My neighbours must be able to hear, she is very loud and high pitched just like a baby. Is there anything I can do to comfort her when I'm not there? She had plenty of toys & hiding places/blankets. Any advice would be very helpful!! Thanks