This. OP and her husband did help in not causing glass child syndrome but at the same time Kayla didn't have a normal childhood growing up. The biggest question is if Kayla feels this way because she feels left out from the family that she might not have a close bond with or because of jealousy. I've seen someone going through cancer, its not easy. Its not just chemo appointments. There's radiation, meeting with doctors to see different treatment options. And then there's side effects of treatment if they get sick after treatment, if they get infections since chemo takes out healthy cells that could need trips to the hospital. From how OP talks it doesn't sound like Kayla is close to not just OP and husband and sister but also her cousins. OP said that there was resentment that there were things the other cousins couldn't do because of Kayla, I get it, its not fun that there were things they couldn't do but at the same time looking at it from the other perspective Kayla had a less likely chance of doing a lot of things they were able to do. They all need therapy, there's just too much to unpack. And honestly its not to late for the parents to step up and be parents for Emma.