Leghorn With Brain damage?

Hello We have a sick hen named Siri and about a month ago we noticed that she was sleeping lying under a shovel we have back by the coop. That day was hot so we picked her up and put her by the water dish. She drank on her own then a half an hour later we came back and she hadn't moved. So we just thought she was tired and she had not showed any sign that she had heat stroke.That night we put her in the coop with cricket (Our other chicken) that morning she was coming out from the hen house and we look up there she was kind of panting & had her wings out & was still sleeping also not eating or drinking. Then we moved her in the house hour or so passed and she laid an egg and we started syringe feeding her. Two days passed still no improvement so we called the vet took her there they looked her over and said keep doing what we are and go from there and she can't hold her neck up and keeps flicking it around in circles i personally think she had got heat stroke and then it resulted in brain damage.We have tried/read everything and i can't believe she has lasted this long and nobody knows what she has I am posting this just for suggestions and opinions about this. thank you for reading have a nice day