Hi MommyDee, when my children were 6 they both (and each in their own way) had a bout of what at the Waldorf school they called the "six-year change". It's almost like a harbinger of the teenage change: they get moodier, and sassier, etc. I suppose just the changing of the teeth can be enough to put anyone on edge :-) Looking back, I realise I had it really bad myself: the whole world suddenly seemed like a dark place; and then my grandmother died. I went into a tailspin, crying all the time; went from a star student to failing grades, etc.
What I'm trying to say is that your daughter is not alone in going through this change; she may be on the young side of the average, perhaps triggered by your family circumstances, but lots of us go through it - and emerge stronger. Keep an eye on her but stop worrying, and just give her lots of love until she pulls out. This too will pass. Oh, and getting enough sleep helps a lot.
(Headsup: there is another episode at 9 years, when a lot of children start to wake up to their individuality - basically one day you wake up and realise that your umbilical cord is gone - scares the living daylights out of most of us! Mine got really scared of everything, they were cold ALL the time, and it was as if they grew velcro and just wanted to cling to me. That too passed. And then of course there is the one at 13-14years *oh boy* ).