Entire body Spasms
Thanks for posting the video.
It looks like Marek's in my opinion. Someone else may have a better idea or insight.
The vitamins, minerals, electrolytes and silver biotic will give her supportive care, but there is no cure for Marek's.
There is always a possibility she may recover, time will tell. The best you can do is keep doing what you are doing and making sure she keeps hydrated and eats.
I do highly recommend you read the first link below, it is lengthy, but is packed with helpful information so you know what you are dealing with. If she recovers she will be a carrier for life and the illness can be transmitted to any other chickens you currently have (those are most likely exposed already) and any chickens that are introduced in the future.
If she doesn't make it I recommend you send her for necropsy so you can get confirmation on whether or not it truly is Marek's, this will give you peace of mind, as well as knowing exactly what illness you have and how to try to control it.
Here is more info on Marek's and some videos that show Marek's chickens as well.