Please, please don't do it. I'm assuming from your username (only saw 5 minutes of the film and it really scared me!) that you are in the UK? Have you any idea how many puppies - pure bred and mixed breed - end up in rescue, or the pound or are put to sleep day after day? Maybe "years ago" less dogs were abandoned or maybe we just didn't know what was going on but the truth is that in the UK today one in every three puppies in every litter ends up in rescue or being pts because the original owner no longer wants it.
I am sure it was fun to have a litter of puppies running around the house - but is that really justification for adding to the dog population? If your motivation is to have a litter of puppies to care for for a couple of months why not contact a rescue and offer to foster a pregnant bitch or a bitch with pups? That way you get all the fun of the puppies and none of the expense and the rescue will be responsible for homing them afterwards.
I don't know whereabouts in the UK you are but I know that Many Tears in West Wales puts dogs in foster throughout the UK
Dogs looking for homes - Many Tears Animal Rescue
But as for breeding your mixed breed girl - you will not find any responsible owner who would be willing for their dog to mate with her.