My bitch had meningitis as a pup twice! We nearly lost her the first time because as you say Sierra she had a stiff neck and was initially treated for 2 weeks for a slipped disc. She was hospitalised on a drip for a week, they did a spinal tap and she was given broad spectrum antibiotics and when given steriods she responded very well. Vets came to the conclusion that it was a steriod responsive meningitis.
However, she is now immunodeficient, of course we don't know for certain that it was the meningitis that caused this because she was only 7 months old her immunity had never been checked eg. titre test. It could have been her puppy vaccinations. She also had a lot of muscle wasteage on her right hind leg, that has improved as the nerve slowly repaired itself, also her right pupil will often stay small when the other one is larger. When it came to booster time we got a titre test done and found that she had natural immunity to parvo and distemper, no immunity to lepto and hepatitis. We keep her on homeopathic vaccines, she gets her lepto once a year because it is a killed vaccine but can't be given any of the other vaccines because they are all live. At the time I called every drug company I could think of and no one could supply a killed vaccine

When she got meningitis the second time she was in her second week of her first season, apparently the immune system can be affected during seasons so we got her speyed meaning she only had one season, we couldn't take any chances. The second time she only stayed in hospital overnight as we instantly recognised the signs and she was treated within a couple of hours.
We are now very careful with her as she is extra special, we keep a stock of synulox just incase she looks like she is going downhill. She is now 3 years old and I keep my fingers crossed she will be with us for many years to come.
I would certainly be interested on anyone elses experiences of meningitis or immunodeficiency. I'm afraid that even though we saw a specialist they still don't know as much as they would like.