Hi - these are the more serious low blood sugar reactions. They sometimes come on so quickly, there is not alot of time before one becomes incapacitated. I have had my share of them and they are scary at first but rarely have any lasting effects.
When the body is deprived of fuel, as all energy is now being sourced to core body funtions, the limbs will clench and spasm like crazy. The mind is still active, hence you could sense that she was aware of her surroundings, however there is not enough fuel to facilitate speaking, or much thought for that matter.
You may want to get a prescription for Glucagon which is a shot that you can give her to stimulate the liver to release stored glucose, enough to stop the spasms and let her eat a carb/protein combination snack.
Unfortunately, as long as the 'normal' blood sugars are within range, these odd ones may happen. It sounds like she is having too many lows so maybe talk to her doctor to see if she needs adjustments, or a completely different kind of insulin altogether, and get a prescription for the Glucagon.
Good luck and take care :)