As rivals said having her own baby might help

Special time when she is able to touch/hold baby

We had to set up the portacot as a safe place to put DD2 in when we needed to go to the toilet etc and she was awake. When she was asleep I popped her in the bassinet and wheeled it into our room and shut the baby gate so DD1 couldn't disturb her. DD1 loved to help get nappies, wipes and her favourite was helping pick out clothes for the baby

It's hard but the novelty wears off and by about eight weeks dd1 was less interested in her little sister. Luckily this time round the bigger age gap has made it slightly easier.