Cassiopeia desperada skin should look like a diamond back rattlesnake not whatever it is now...
During the 2014 skin update it was clear the color change was necessary to better match the new color palate being used in the new summoners rift map. However somewhere along the line Desperada got taken from a venomous desert looking rattle snake to a look that only could resemble a non-venomous snake with a rattle thrown on the tail.
Don't get me wrong, the portion of the update that changed her clothing, body, hat, and rattle on tail all look Great! I am specifically talking about the rings on the snake portion of her body. They do not resemble any snake breed I am familiar with and look nothing like a rattle snake (rattlesnake specifically some type of diamond back rattle snake is what I think the desperada skin theme should be modeled after).
The western themed skin should be patterned similar to this next link (specifically notice the dark diamond with light white colored borders around the diamonds): http://www.ourbreathingplanet.com/wp-content/uploads/2014/08/31.png
Her current body looks like this patterning(not the color just the pattern): http://www.californiaherps.com/snakes/images/cooccipitaliskc6102.jpg
TLDR; If you are going to make a western themed skin for her, you need to use a pattern from the deadliest snake in the west the diamond back rattlesnake. Otherwise the theme doesn't make sense.
Edit: just want to make clear that the rattle snake skin I suggest does not need to be as complex as the diamondback picture seen above. I think simply doing the diamond pattern that runs down the center of the snakes back would be enough identity to the diamond back rattle snake to be a simplistic yet thematic look for the skin.