Sounds like her previous home was not a good one seen as she was all matted and the lady saw fit to sell/give her away when she maybe pregnant
The pup is glad she is now with you who will care for her properly.
Is the 26th the soonest appointment you can get with the vet? I would recommend pleading for a sooner one or going to a different vet because if she is pregnant it only gives you 2 days to prepare for the pups!
I hope all is well and good luck x