Sarah, first I need to apologize for getting your birds mixed up.....it is Gracie that had the frost bite...not Sunny...
Ok...when you did the exam, did it feel like you were hitting a wall with your finger...like it was firm but seemed to end there, may be turn down to the left or right?? If so, you were in the intestines. An egg feels like an egg.. you can twirl your finger around the top of the egg and it feels hard. Generally if your finger isn't able to go straight back and it seems to want to go down, you are in the intestinal tract. If there is an egg right there, you can only go straight back. No shelled eggs feel like an egg without a shell and are very soft. If she has an egg present, you can't enter the intestines easily. If no egg is present, then you can't go into the oviduct easily.
As for a seizure, you can only watch them to know they are having one. Usually they go stiff on one side and will fall over. They don't last really long, but they will want to sleep for hours afterwards.
A stroke generally leaves them with the inability to do something, whether that be walk properly, hold their head up, breathing funny, not be able eat or drink, etc...Stroke takes a while to get over. Miss Molly took a couple months to get over her walking issues and her heart and lungs never did repair.
So if Sunny were my bird, I would keep her inside tonight somewhere dark and quiet. See if you can get her to eat. Anything. It doesn't have to even be chicken feed. Just something to stabilize the blood sugar in the brain. Then in the morning if she is able to stand up, wants to eat and drink, take her out to the coop, but I would keep her confined for that day. I would take this day by day. Let her out when you are around so you can watch her. If she returns back to normal in a couple days. than I doubt she had a stroke. If this was possibly a seizure, she may have another or maybe never have one again. But if this does happen again in the next days or weeks, then I would say yes she is having seizures. Strokes will leave longer lasting effects on the body.
Just take this one day at a time and make a decision each day as to where she is at and how she is healing and what to do for her. You know where I am and can PM me any time.