I have 3 DC - DS who is 6, DD1 is 3 (nearly 4) and DD2 is 3 months.
DD1 has firmly had her nose put out of joint by the arrival of her sister. She loves her immensely but her behaviour is awful! I know she is attention seeking but her constant poking, prodding and yelling at the baby is wearing me down and I feel like DD1 feels very alone as all I seem to do is tell her off 
I try my hardest to praise her when she is being kind and gentle but it feels like there is a bit of a gulf between us and I don't know how to bridge it!
Am I totally useless for not knowing how to start to deal with this? My 'let's be positive and be friends today' attitude never seems to last past breakfast!