I would guess she was sick from the heat, and after it happens once, it's more likely to happen again. I don't think free ranging in 104 degree temps is going to make her feel cooler. You might put a shallow pan of water out in the shade so they can stand in it and cool their feet. Cooling feet makes the body feel cooler. But if she is susceptible to heat issues, I would put her in the basement in a crate or in your house on the bad heat days. Silkies are not the most rugged breed and are affected by weather extremes up or down.