Sorry about what happened. I know that was a horrific thing to witness, as it has happened to me too. Well, something similar:
My daughter was 3 and she once was walking a bit too close to the swings at a park and the when the person swung back, they slammed into her and sent her flying and she landed on her back. I saw it happen, I was pretty close by, and ran over to her. I did the absolute wrong thing and grabbed her in my arms. She tried to scream, opened her mouth and no sound came out. That terrified me. Then her eyes rolled back and she had a look I had never seen her have before.
One of my friends was at the park as well and was an ER nurse, so I immediately ran to her with my daughter in my arms. She took one look and said "just hold her, she's having a seizure". I was flipped, but tried to stay calm. It only lasted several seconds and then she came to.
My friend called the hospital she worked at for us to immediately come in for a CT. Turns out she was fine, no damage to her brain at all.
So I think it is possible for this to happen.
Wishing the best for your GF and you.