It's good to see that you have gotten so much good info and advice. Great advice from Greysmom about watching Bella around Angel.
This could very well be a "one-off" for Angel, and hopefully, it is. I would imagine Bella is picking up on your anxiety level. Not only is her sister not there, but Mom is upset. I know it's not easy, but try and be as calm as you can around her.
I've never had a Grey with seizures, but have had 3 cats who had them. Oh, my gosh, I understand how scary they are, especially the first time you see your baby so out of control. But they came out of them without complications, and due to the infrequency, they didn't have to be on any meds. If they are put on meds too soon, you can't really know if the seizures are controlled because of the meds, or if they just aren't having any on a frequent basis. Best to give them the benefit of the doubt, especially when dealing with meds that could have unwanted side effects.
We're all thinking about you and Angel, and sending out lots of good thoughts. Hope she can come home soon. Please let us know how she's doing.