New GSD mixing with current dog (diff breed)

Question
We have recently purchased a female 3yr Pedigree GSD from a family friend who can no longer look after the GSD as they are growing their family. The GSD is disciplined but yet loving and playful. we introduced her to our current dog which is a Chihuahua crossed with a jack Russell, the GSD was very excited and just wanted to play but my poor little Chihuahua cross was terrified. The Chihuahua cross is usually quite protective as it is and did start to grizzle a little bit when she felt i was in danger. i am just petrified that the GSD might attack her if we are not around as she may get territorial. i am sure the little one will adapt shortly and feel more comfortable when she realizes she is not in harm...but could she be in harm. Please shed some light!

Answer
Since it is the smaller dog that doesn't want to play, I doubt there is too much danger. I would keep an eye of things and perhaps not leave them alone together until they are better sorted out.  Crating one or both might be the best way.  Other dogs may
not be as bad as the young Labs I am plagued with.  Still your house and dog
will be much safer with the dog in a crate when you are away.  The dog may be
happier in its den than loose in the house.  It relaxes, it feels safe in its
den.  It rests, the body slows down reducing the need for water and relieving
its self.  Dogs that have been crated all along do very well.  Many of them
will rest in their crates even when the door is open.  I think the plastic
ones give the dog more of a safe, enclosed den feeling.  They are harder for
dogs to open too.    Metal ones can be put in a corner or covered with
something the dog can't pull in and chew.  Select a crate just big enough for the full grown dog to stretch out in.

Leave it some toys.  Perhaps a Kong filled with peanut butter.  Don't leave
anything in the crate the dog might chew up.  It will do fine without even any
bedding.  You will come home to a safe dog and a house you can enjoy.

A dog that has not been crated since it was little, make take some work.
Start out just putting its toys and treats in the crate.  Praise it for going
in.  If you have been able to trust it with any bedding, put that in the crate.
Feed it in the crate.  This is also an easy way to maintain order at feeding
time for more than one dog.