Most good breeders will never let a puppy go to a home for Christmas. This is of course to stop people impulse buying. Christmas and all its excitement is not a suitable time to introduce a pup. I am sure you are not doing this, but puppies should never be a surprise gift. Looking after a pup is very different to looking after the old dog, and your mum needs to be able to decide if she can take this on. Having said that, if your mum wants a pup, why dont you reserve one, and her xmas gift can be a collar and lead in a box with the "promise" of her choice of pup/dog to follow.
I hope you have success in finding a new companion for your mum.