barbara, it's really difficult to tell from your description if savannah is dominant or fearful. maybe if you could describe more her body language in various situations we could help you evaluate. she sounds very aggressive, but it also sounds like you know how to handle her. she would be too much for me.
how is she with you? any dominance displayed towards you or your family? or is it just with strangers?
if her aggression is a symptom of very high drive, why not exercise her very hard. do you run or ride or horses? bicycle? is her OB good enough that you could take her on long horseback or bike rides? i know further east of you there are some very nice state parks. might be worth a drive 2-3x a week. ben also has high drive, and we take him on hikes up steep mountains a few times a week to wear him out. it's good for us, too!
hope you find a good trainer for her.
ben aced his CGC at the age of six months, then he started showing fear in situations he'd never shown it before. in retrospect, i think it was adolescence, because he has really settled down a lot in the past six months to a year (he's now 3 1/2 yrs). his vet and i were talking about it the other day; she noted he had the potential to become a fear-aggressive dog during his adolescence, but she thinks he's fine and quite trustworthy now. we worked a lot with him to build up his confidence, and it paid off. this is the first time i've had a dog that needed special handling, so we may have made some mistakes with him until we understood what we were dealing with.
he remains aloof towards strangers. if someone comes into our home, he'll sit/stay on command and let me handle it, and then on his own terms, in his own time, he'll approach the stranger and check them out. he also doesn't like people looking in his eyes, but it won't provoke aggression, just backing off. some people he even wants them to pet him. but he's very particular, other people he will run away from. he's just not a very sociable guy when it comes to strange humans. he loves other dogs though!
he'd be fine on ignoring a neutral stranger, as long as they ignore him. he doesn't like unsolicited attention.
he sometimes startles when a bicycle or runner comes up from behind, though not always. he does recover, though. he's also been known to try to give chase! usually he seems to be playing when he does this. though if he's in heel, he looks to me in the presence of any distractions. he probably would display avoidance walking through a crowd, especially if people paid him attention.
if he's put in a sit or down, he will hold it until hell or high water no matter what approaches him, though if it is another dog, he will never be indifferent. he'd probably tremble with excitement, wanting to play, and look to me for a release. he's been trained to sit/stay on walks with other dogs to play with as a reward.
so, in the first part, the main risk is that he will spook. he's pretty spooky and shy. otoh, sometimes he just isn't paying attention and would give them perfect indifference.
in the second part, he would definitely lunge and warn the assailant off, but if pressed hard, he might go into avoidance. 50/50 if he will out and heel after being so heavily stimulated. and the part i am really unsure of him is at the end, where after all that intensity, he is expected to be calm in the face of the judge. when ben has been highly stressed, he can stay that way for quite a while. if he gets reactive, he often continues to be reactive.
just to be clear, this is NOT your typical mastiff temperament, nor is it typical of his line. he's been very slow to mature, and he's been steadily improving and calming down. i trust him now with people, whereas a year ago i didn't. heck, the mailman can come into the yard now and he doesn't even look up. friends let themselves into the yard and come to the back door and he barks a warning, but he no longer does the fear-aggressive lunges he was doing as a teen. so, we hope he's growing out of it. he's still very puppyish in a lot of ways, and evidently this line is slow to mature both physically and emotionally.
your girl may also "even out" as she matures. hope so, she sounds like she has a lot of good points.
working Mastiff