I think they need to ensure that they plan in some time just for her as often as possible. Half an hour of special time from one parent...very regularly. Get her to help with baby whenever it is possible. [collecting/holding things for mum/dad; sitting at one end of bath with baby in baby bath in bath, held by mum/dad...gently pouring water on her baby] Explain why baby is crying, explain that she cant talk yet so cries to express herself. Talk about how she can express her feelings. When crying and screaming, acknowledge she is upset, ask if she wants a cuddle, instead of asking what is the matter. Just cuddle her and acknowledge that she is upset. Make her feel special every way they can but most of all ensure she has regular bursts of individual attention.
My son was 21 months when his sister was born. All the above tactics helped him.
“We start school too early in the UK!”
I hope the new PM is kind to Larry the Cat



