Autistic and other disabled children aren’t “burdens.” It’s fair to say it’s Molly’s responsibility to show/teach Kelly how to care for her kid. It’s not unfair of Molly to expect Kelly to learn how to help provide some care for her child if they are in a committed relationship and especially if they are living together. It’s not appropriate to pass judgment on the behavior of any young child, let alone a disabled child for whom emotional dysregulation is likely a symptom of their disability. If Kelly doesn’t want to learn or provide any care, that’s fine, but that is a reasonable dealbreaker for the parent of a disabled kid to have. I’m not saying the partner should be expected to devote themselves full time to caregiving, but it’s a reasonable expectation for them to help sometimes.