Why is Heather not in prison for murdering her family?
Ask yourself - why is Winter Soldier not in prison for murdering Nomad?
Apparently if you're brain washed, you're not held liable for your actions, and free to go.

Where is her daughter now?
I suspect that might have something to do with the big fight her and Mac had. Or at least, I hope it does.

Why did Mac take her back?
Because she was brain washed, and was not herself.

Why is Guardian's leaf upside down in this cover?
They're in the spirit world. Everything's backwards. Like looking in a mirror.
Or something.

Those are my guesses! (Well except for the last one, I think Phil may be more correct than I am...)