It sounds like she wants to be available to you anytime, but she's having her own overload issues. No matter how caring a person is, there have to be points where they can't take care of everything! It would be useful to know what your concern was when you called her, and how long you waited before calling again.
I myself don't have "nephew on drugs, a niece with adhd, a lot of sick people in my family, 3 kids, a husband, 5 grandkids". That would be too much for me right there. I can barely keep sane with my own lesser issues. If I had all that going on in my life, I would be screaming, slamming, throwing, and stalking out all the time. My blood pressure would go so high, I'd do like a cartoon thermometer that explodes out the top. Think about how it would be for you if every time you turned around somebody was in your face desperately needing something from you, and your full attention. And being the go-to person for everybody's troubles. Women are expected to be the big nurterer, and most of us fall into that pattern more than we should. Even I do. But I need plenty of alone time to maintain my sanity, and it sounds as if she probably isn't getting any!
Without knowing why you needed to talk to her so urgently, I would suggest maybe leaving her a message to get back to you when she can, with maybe a hint of what it's about, and then go play some computer games or crank up your headphones with some good Bach or something. That always gets my brainwaves properly aligned, anyway.