I know its slightly off subject, but i have seen it written many times on the forum that it is terrible that a pup leaves the litter prior to 8 weeks, I believe this to be untrue, my husband and myself always get or pups at 6 weeks. I have found it to be damaging for the pup to stay longer than this in certain cases, i.e. large boisterous litters or quiet environments. A strong fully weaned pup at the age of six weeks settles in very quickly, especially if the breeder has done their work on establishing a coping strategy in the dog for being left alone for small periods of time, they tend to be friendly with other dogs, but not boisterous, nervous, or obsessed, as long as you got a good pup in the first place and continued to socialise it correctly.

Back to the actual question, Molly has gone from a quiet environment into a busy one, none of her training was sound enough to carry through strongly in the new environment, nothing you'd done wrong, just didn't have enough time.

Continue with your training of yours and your mums pup, on their own at first, without the distractions of the other dogs.
Once that seems to be going really well have the quietest calmest dog in the room laid down while you train the pup.
Gradually up the criteria to other areas or extra dogs, if you start to see a breakdown in your training, you have just gone too far too soon, go back to the previous step.

I don't envy you training two pups its hard work.

Your pup is probably just confused about toilet training, stay out with her until shes been, even if it takes an hour so you can praise, at least its nice weather at the moment, its much worse if its raining or snowing.

Good luck with you training.