How to deal with daughters jealously?

ok long story short I take care of my two nieces, have for seven years now, raising them as my own, they are now seven and ten, I wasnt going to have any children of my own because I have the girls, well unplanned stuff happens and I now have a 6 month old baby boy, my oldest girl adores him, always wants to help me take care of him i actually have to make her go and play so she can be a kid, well the 7 year old is real jealous of him, she doesnt really want to be around him at all and i think she is mad because he is always with me, its not like i can leave him by himself, i have tried to do stuff just with her but my husband cant keep the baby calm so i end up back with the baby, and i have tried to get her to do stuff with me and the baby and she wont she will just go into the other room, i dont know what to do to make her know that the baby isnt a threat to her, i tell her i love her atleast twice a day and try to include her in everything i just dont know what else to do, any ideas will be helpful, thanks