Adopting from a single dying parent while fostering?

I'm named as guardian for my youngest sibling (still a minor) in my parents will. My understanding is that if anything happens to them, she would come live here without any fuss or much paperwork. That's why people name guardians, right? Of course, then I'd have to update my home study for fostering to reflect that she's here. And her moving in might be considered a major life event where I would have to wait a while before fostering again or something.