Oh the joys of puppies expanding their horizons! My puppy had a different experience when she was "growing" (she still is!) but the end result was the same ... scrapping and sometimes a brawl.
For your situation, I would do some leash walking with her in a place (not necessarily an off leash park at this stage) but walk where there are lots of other dogs on leash. Let her sniff, count to 5 or 6 and move on. Same thing with the next dog. This way all of her introductions are ending on positive notes. Praise how you see fit.
From your post, you seem to recognize the split second when she's about to "pull that switch" ... once you've had lots of positive 5-6 second introductions ... let them go a bit longer and then interrupt her behaviour that split second before she can "pull that switch". This way you are letting her know EXACTLY what you want from her. Polite intros are great, sniffing (since you've praised her) and then the interruptions just before she does the unwanted behaviour.
Depending on the dog, I've used a variety of methods when I've interrupted behaviour, a strong NO can be very effective. Some dogs take to this correction very quickly, others might cringe at the vocalization (or they'll talk back, they are GSDs after all, and sass is their middle name). I wouldn't use a "super strong" correction at this point because you are teaching what you want / don't want. By super strong, I mean prong / choke correction.
HOWEVER, if after a series of "minor" corrections, your dog is still not getting it, you will, of course, have to up the seriousness of the correction.
It's so hard to try and give suggestions / information on line because you can't see exactly what the dog is doing. The other thing to take into consideration is the behaviour of the other dog. At 10 months, your pup's not old enough / lacks worldly experience to get all the tricks of the trade of being a dog. She might sense that something's "off" with a dog, but might not have the "right" answer in her brain, and this can cause a scuffle.
Also, in providing this information, it's simply a guideline as you know your dog better than anyone else. For me, when I'm working with my small zoo, whenever there's an unwanted behaviour that pops up, I reevaluate everything I've done / haven't done, and go back to the basics.
Lots of luck, and please post back results, I love to read follow up stories.