1) Jurisdiction in such cases not established by residency. Otherwise this could have been promptly dismissed, and CT wouldn't be able to decline. But MA can't go into CT and investigate - only refer to CT. But she wasn't removed due to her home life, so that's a non-issue. If you live in CT and enter MA right now and are witnessed abusing your child, for example, MA social services would be the only ones with authority to respond. They would take the child if you were alone, and then talk to CT and usually transfer the child to CT, who would then investigate further and either find a family placement, put the child in foster care, or work on reunification. If the child's dad lived in Texas and did not have custodial rights, MA would probably get in touch with CPS there instead and let them look into the dad, and arrange a transfer if it looks like the dad will take custody. Etc. And if you got out of jail and wanted to challenge the decision, you would file either in the CT family court or the family court where the dad lives, and deal with CPS in that state as part of the case. If no one stepped forward showing any interest in the child and you remained in jail, MA would just retain custody of the child.
If you wanted to bring some sort of civil rights suit for wrongful CPS action, you'd have to sue the MA authority since they had original responsibility for the issue. You couldn't sue CT CPS until they agreed to get involved.
2) And there is no way Children's is letting her die of fatal mito complications - I mean, talk about liability. If she's actually having symptoms that could be fatal, they are not treating them as in her head. You can't have a stroke due to somatoform disorder. Gastrointestinal issues and pain could be caused by either, but neither kill alone without a clear warning the problem isn't mental. And there are almost no treatments, so what do you think they should be doing? The recommended treatments are aimed at symptom control and stabilization, not stopping fatal complications.