
Most of what you say is normal with the caution that all bitches can be 'different' even with the same bitch but different litters.
The fact you fed liver could well account for the colour, if not the consistency of her stool output. Why the 'puppy mix'? That's for PUPPIES, not for mums. The puppies will take what they need - both pre and post whelping and there's no need to be vastly altering what mum has, at least not until you see how many puppies she has to cater for, when you up her intake, or not. Again all our bitches had their normal food throughout pregnancy and beyond, perhaps cutting back on the bulk (kibble) as the unborn puppies grew bigger, in favour of just meat. I'd avoid liver.
Once the demands of her puppies, when born, increase - into the second week, then you up her nourishment, again or not, depending on how many puppies.
She'll produce these puppies when she's good and ready .... it's all too easy to become overly stressed during these final hours

Just don't leave her much over 62 days without anything happening. Your stress won't help her!