I can only give you some suggestions:-
If she is an ex puppy farm dog she would more than likely be traumatised to now be in the outside world, which would explain her timid behaviour & possibly not eating well.

Regarding wether she is pregnant, they don't normally increase in size until 5/6 wks approx. A vet would be able to tell you by examining her at about this stage or a scan will confirm at 4/5 wks too.
She could be having a phantom pregnancy, which can occur approx. 7/8 wks post season. This could also explain why she is producing milk.

Imho its impossible for anyone via a forum to know if she is pregnant &
the best route is to take her to the vets asap. If she is pregnant she may not even be healthy enough to carry or give birth to the puppies,
so her life may be at risk.
I also would be surprised that a puppy farm would release her if they knew she was pregnant because these poor dogs are just used for money making & hence they would have lost some of their 'precious' income.
This also makes me concerned that she might have other health issue's