Question concerning Lack of Socialization
"In your opinion, can any problem with a GSD be dealt with, and is 9 months too old to start training?
I have a female that due to health problems missed out on a lot (not all) of her socialization, she seems nervous and not over lean on other dogs."
Spelling has been corrected to suffice search engine requirements!
Some parts of your question are not understandable, particularly the last part "she seems nervous and not over lean on other dogs"? I'll try my best to be more precise nonetheless.
"Can any problem with a GSD be dealt with?"
No way! Got a problem?? See here what to do.
"Is 9 months too old to start training?"
Waayyy tooo old, yes! See here what to do.
Where would we all be without some FUN joining our problems, huh?
So, you have a 9 months old female German Shepherd puppy, and the dog missed out on a lot of socialization, and you are wondering if you can still save the situation?
Socializing your dog is never too late, the Puppy 101 makes the point, it just requires ever more effort the later you start. Start?? Yes, socialization never ends.
The problem with a 9 months old puppy - and likewise with an adult dog - is: The what's called facilitation slows down from an "explosion" at say age 5 weeks to age 6 months to a sluggish snail pace later. Some people say "priming" but that doesn't quite fit the bill of facilitation:
Every thought and every decision and every move you make and all your behavior is instigated by nerve impulses (a tiny "electrical current" running through the nervous system). This is the same for dogs. You follow me so far, right?
Now, nerve impulses can only transmit from a certain nerve axon to a certain nerve axon ... if the axons are connected, right!
Depending on which axons connect, and how many and where ... certain thoughts, decisions, and body movements will be facilitated (possible) - or not! You (and your dog) will be able to think through (mark the terminology) certain thoughts (and so to come up with a solution), to make certain decisions, to move your body in certain ways and at a certain speed, etc - or you (and your dog) will not be able.
That's why this nervous system development where axons grow to form new connections is called facilitation.
In short: Everything you do today (and what you don't do), your job, your hobbies, your abilities, your successes and your failures, your pain and joys, your wealth or scarcity, all your thoughts and behavior that have led to where and who you are today ... is the result of how your nerve axons connected during your childhood, and during drastic changes in your life. The same with dogs.
Now, when you have a young puppy or when you get a rescue dog, because everything is new, a multitude of new sensory sensations is irrupting into the body (through ears, eyes, nose, taste, sense of touch) - and they have to go somewhere, right? This is why a young puppy - and a bit less so a rescue dog coming into a new environment - experience an "explosion" of new connections being formed. New thoughts and behaviors being facilitated, to be easier later - because the connections have been established.
Frankly, at age 9 months I doubt there will be much of an "explosion" of new neuronal connections forming in your puppy's nervous system. Clearly new connections will still be made, but not so many, and more like at a snail's pace.
Meaning: You can (and should!) still shape your dog's behavior going forward through comprehensive socialization NOW, yet it will take longer and more repetitions before the right new axon connections establish, and thus before your dog will behave the way you want.
Conversely, what will happen if you wait a bit longer because you think "it's too late now anyway"? Then obviously your dog will be less accustomed to new situations and environments (or not accustomed at all), and so what you call "dog behavior problems" those will increase. The typical end result of a lack of socialization I showed you in this dog question and answer. A poor outcome really, for both dog and dog owner!
So yes, socialize your 9 months old puppy now immediately, and not only with other dogs (yet primarily). - How? I would assume the Puppy Development Guide - Puppy 101 is a great, extensive reference guide what to do, when, how, how much, and why. When you've read the book and you think it's not, let me know here why you think that.
If you are not into pure reading though, maybe seeing it all in Multimedia Puppy Chronicles is what you were missing until now?