I have recently got a 12 week old GSD. I deliberatley got a puppy so he would be the same size as my cat initially so he wouldnt intimidate her. I got her back in march and she is wonderful. However ever since i brought him home two weeks ago she has avoided the house and will not come indoors. I have tried keeping her in for a few days which kind of worked but as soon as the door was opened she shot out. At the moment i cant help but think im going to lose her.
When i get the chance i go outside without him to try and offer her some affection when shes around. The last few nights i have put food out for her as am getting very concerned.
He has barked a few times at her and chased her up the garden in a playful manner.
Please, please i need ideas before i lose my cat, many thanks

It is quite normal for a puppy to chase a cat the initial introduction matters greatly if puppy just wandered in as this massive puppy bounded over to her she is going to be frightened.
You are going to have to start again with cat bring her in and make her bed upstairs away from the puppy feed her there and dont let her out for a good few days until she settles back into her own home give her treats and things she loves to make her feel safe.When you feel that you have accompished this (not forgetting that she wont have forgotten about the puppy)
I would get a crate for the puppy and bring the cat in offer her food and some milk or cream things they love.
let her wander around the puppy while she is in her crate let her investigate if puppy gets too excited give her a handful of treats while in her crate so that she sees cat as a good thing I personally would put a gate on the stairs so that cat has an escape route.... introduce them  this way for a good while then gradually let puppy out of crate while cat is still in the room possibly on a lead with treats for puppy ....introducing them slowly.
Normally I would say leave them too it as they will work it out between them usually cat gives a good whack on the nose of pup and that is enough to make thier boundries ...but in this case I think cat has had a fright and may need some extra care.

hth I have 3 cats and 2 dogs the cats are definitely in charge!!
~Roni