You say you don't understand the hysterical reaction OP. Answer: you don't have to, you just has to respect others don't feel like you do about your ddog.
she lost her shit [when ddog jumped up]
Well clearly you lost your shit a bit there that you couldn't rationalise that this move was clearly completely unexpected and the DC had no idea what would be happening next. Previously she hadn't shown any fear and had been happy with your ddog around, so she wasn't primed for fear, your ddog did that. Well no, its never the ddog to blame, its the owner.
Can you please explain why you have not left your dpup off the lead yet? You blamenit on it age, when that's not a good reason. If your dpup did enough running around off lead, it might be more relaxed and tired. It should absolutely not be left to play around young DC, it absolutely will get excited.
It's important for you to realise that a dpup does not have to have a nasty or aggressive temperament to seriously harm a DC, its just that dpups and ddog in general are very tuned into excitement, that includes DC dancing about, playing, running, high pitched voices; to a ddog these are triggers for ddogs, and inexperienced or youngsters will react with equal or greater excitement, demo strated as leaping up, scratching, snapping, biting, tugging, gripping with teeth, shaking.
It was your sole responsibility to keep the dpup away from such a young DC, and only allow it around those it is used to. Your dpup, just because of its age could easily have snapped at her face in excitement, caught her cheek, her eyes, torn her nose.
Without you wanting it to be, or believing your dpup has harmful intentions, it doesn't from what you've said, regardless it still is absolutely a risk