You’ll never be able to discover her exact mix, if they didn’t see the Golden mate another dog. You might as well just love her for the cutie pie that she is.
Also - puppies are babies. They’ll poop almost anywhere. They’ll do disgusting stuff, then want to lick you afterward. THink about it this way - the mother cleans the new pups up by licking their butts - they can’t find it too disgusting. Just try to get her housebroken as soon as you can. That young, it’ll probably take a bit of time. I hope you’re home most of the time so you can take her out regularly. Crate training (understanding that she can’t hold it all day at this age) is your best bet.
We’ve had two guide dog Golden puppies, and we got to play with our breeder’s puppies, and the only thing I see different from them is the maybe short ears. On the other hand, it seems that it is hard to tell. Our pet dog is a Cocker Spaniel /Border Collie mix, but his papers say cockapoo - and they docked his tail when he was a puppy thinking that.
Dogs seem fascinated by other dogs poop. You need to correct them when they sniff it, for health reasons at least.
We trained our guide dog puppies the official way, which is taking them out to go when you think they should be ready and telling them to “do your business” when they go. This way they associate the words with going, and you can get them to go on command. It really works.
5-6 weeks? Lordy. Do you know any breeders around who might have a litter you can socialize this one with? 5-12 weeks is CRUCIAL timing for dog social-skills. Any chance you can get her back to her mom for two more weeks, anyhow?
No idea on the breeds, probably won’t even be able to guess until the dog is half-grown, at least! Sure is cute, though. Whisker length can vary from dog to dog within a purebred litter. Feet DO look smallish, but the pup is so young… And, color of littermates doesn’t matter - there can be more than one father to a litter.