How can we help our daughter be nice to her sister, who has cancer?

i have a daughter called jade, whose mother died shortly after she was born. i brought her up. she is now six. i recently met a woman named rose, who is also a single parent. rose has a daughter called nicole, who is four. we got married and became a family. we adopted eachother`s children. adjusting to a new mother and sister haven`t been easy for jade. i had spoiled her a great deal. nicole had also been greatly spoiled by her mother. jade and nicole did not get along very well. nicole often tattled on jade and got her into trouble. jade thought nicole was an annoying little sister. unfortunately, jade got cancer and was in the hospital for ages. she had to undergo many treatments, including chemotherapy, which made all her curly hair fall out. when she got home, people gave her most of the attention, which made nicole jealous. when we go out as a family, jade might not be feeling well and we would have to take her home. nicole would cry and scream because she would want to stay and play. rose and i comfort her by saying" we have to go home now because your sister is tired. we will play later" nicole had now became greatly attention-seeking. how can i make things better? i love both my daughters very much and want them to be happy and comfortable. they both need to be cheered up. jade says she wants to go to disney world because she had never been there. we are not poor or anything, but jade`s treatments are very expensive and we don`t have enough money to sent four people to disney world. how can i make her wish come true? also, rose is now pregnant and there is now a new baby girl on the way. somebody adviced us to enroll nicole at a preschool so she can try new things and have children her own age to play with. we thought that was a good idea as she needed a distraction. she was looking forward to attending when we told her about it after taking her to have a look at the preschool. she was doing pretty well there until a boy there called billy pushed her. billy is a little boy who have pulled her hair and teased her on some other occasions. she didn`t feel safe there anymore and has been telling us she doesn`t want to go. she is begging us not to send her back.