Thank you for your email and congratulations on your baby. I understand how concerned you are feeling.
It appears your daughter is displaying some anxiety, especially with not wanting to share you which can be in anticipation of the new baby. She has begun to realise that her world as she knows it is changing, and that not all the focus is on her anymore. This is making her feel insecure as she would rather not go through these changes and share her mother who has been solely dedicated to her. To paint a picture of how she is feeling it's a bit like your husband saying he's bringing home a new wife in a few months and you should be very excited about it, when you have no control or say in his decision.
While I agree that you want your daughter to be involved in planning for the new baby, as she is still very young I would recommend that you don't take her to every scan and try not to talk too much about the new baby in front of her, but rather keep the focus on her. Continue with her usual routine and reassure her that you love her and that she will always be your first baby and no baby can take her place.
Take your cues from her. If she asks questions about the baby or wants to help decorate the baby's room encourage her by letting her choose some toys, clothes and a special gift for the baby. Also ensure you have gifts to give her from the baby. She will look forward to visiting you and the baby in hospital if she receives a small gift from the baby everyday you are there.
She will need more of your attention as the birth approaches and especially when the baby arrives. Arrange with family members and your maid to be available so you can hand them your baby when you need to focus on your daughter. By keeping your attention on her she will soon adopt the big sister role and be keen to help with the baby.
Good luck with the birth and let me know how you all are doing.