Oh dear, I'm sure you must be feeling shaken up and a bit shocked right now
Sounds like jealousy, especially as you've said that Gemma has been trying to get closer to you lately if Poppy wants a cuddle.
Jealousy isn't unusual and can easily erupt into physical form. I don't know if you normally leave Gemma and Poppy together at night or if you're out in the daytime, but if so I'd change that for the time being and keep them separated when you're not around, just to be on the safe side. Gemma will be in a heightened state of tension right now and that may take a while to diminish.
When Louis was a few months old we had a couple of incidents where William flew at him, growling and barking, and they had a bit of a scuffle. But it was more noise than anything else and definitely no hanging on. I could be wrong here, but the way you describe Gemma's attack as being silent and then holding on to Poppy's ear and not letting go makes me think Gemma meant business. I'm not sure if your comment about spaniel rage means that you're worried that Gemma has it, but I'm sure she hasn't. She sounds as though she was intensely jealous, which is actually a normal dog behaviour although a fairly extreme one sometimes.
I'm hoping somebody with experience of this will comment, but my thoughts are that for now you should keep them separate when they can't be supervised and think about getting a behaviourist in. The last thing you want is for things to escalate so I think you need to act quickly.
Take care of your hand too as even small puncture wounds from a dog tooth can easily become infected.
