The one thing that helped my DD the most was lots of cuddles. We have just gone through the same thing. Dd turned 2, 2 weeks after bub was born. We were getting lots of tanties. It's so hard, please don't beat yourself up, I know the guilt you are feeling. She will be ok. What I did was hug hug hug her any chance I got. As soon as baby was asleep I would cuddle her, tell her how much I loved her, that she was my special girl etc. Let everything else around the house go for a while. When I was BF bub I would have her right next to me if she wanted to be there. I asked her to get nappies, wipes for bub. She had her baby that she would bath while I bathed bub etc. it gets easier. Things are great now. It's also a learning curve for them to learn that sometimes someone else's needs comes before their own and that's ok. Also try and have special time the two of you every day, even if its just half hr. have a bath with her when your partner gets home or a shower. Take her to bed and read stories for half hr while he has bub. Let him do bathtime with bub and you do one on one with your other daughter.