I'm sorry she is not doing well. Hopefully you can see the vet.
If the Scott's multivitamin doesn't contain iron, that would most likely be fine. I would start out by crushing 1/4 of a tablet and adding it to their food.
If made fresh, I don't see any harm in the cucumber water. If you don't have commercial chicken feed available, use egg (you can give them the white and yolk) and you can also use cornmeal wet down to make a mash or it can be boiled a little to make a porridge. Since they are so small if you use something like cracked corn it would need to be soaked or boiled to soften it a little. Only prepare what they will eat in a day so it doesn't spoil.
Sugar water can help give one that is sick a boost. Do the best you can to keep her drinking, keep her warm - your temperature sounds good, but she may need to be in a small box if there is wind.