Not that it excuses her behavior at all, but taking care of a special needs kid (especially one with a profound mobile/intellectual/well, everything impairments) is really fucking hard. Unless you pass off the care to nurses, sitters or respite care, it's a job that never ends, there's no relief. And even with assistance (which I think families are entitled to, especially if they have other children), it's not over. You learn to sleep with 'one eye open', so to speak. (Source: family member with severe Autism. I could power level more, but I won't.). Caring for a child like Kayli also means giving up hopes & dreams. First days of school, dance recitals, first dates, graduation, a wedding, grandchildren, a career. No teaching her how to do her make-up, how to ride a bike or drive a car, no consoling her through her first heartbreak, no prom dress shopping, no college acceptance letters. Hell, even successful potty training isn't something they get to experience. It's a whole different type of grieving and adjusting your expectations. And a lot of people see that having to adjust those expectations as not being fair. "Why did I get a child like this? I've done everything right!"
Some parents think that because they've been dealt this lot in life, they're entitled to/deserve the best or whatever they want or "what their child wants". I guess it's sort of a weird Munchasen by proxy....they aren't hurting their child, they aren't keeping their child in this state, but they crave the attention a MBP parent would. It validates their 'suffering', it gives them an endorphin rush and make them feel like they have a 'normal' child, I guess. Especially if the child's condition is terminal, they want to shove all the 'normal experiences' they can into what time they have and they want it known that they and their child are special & unique & a warrior.
I hope that makes sense. Isolation has caused me to dive deep into parts of the farms I haven't explored before.