With this one there are a few routes you could go down, cheerleader fighting against zombies, cheerleaders already as zombies or cheerleaders who are in the process of becoming zombies.
You can create your own outfit but there are so many awesome cheerleading costumes out there, both media inspired and original for a decent prices (generally less than £25) that you might as well purchase one of those. Check out ebay and amazon for cheaper versions available from fancy dress sites.
If you want you could just go for a simple ra ra or skirt skirt with a top in the similar shade or a contrasting colour and add some writing or imagery to the top. Throw on a hoodie to keep yourself warm :)
Hair, Face & Nails
There are some awesome tutorials on Youtube that sure you how to create the undead/zombie/bloodied victim look. Here are a few of my favourites 1,2 and 3 but I would pick some fake blood, dark red lipstick and dark eye-shadows (browns, purples, reds) to create an undead look, there are a few palettes out there which tick all the boxes.
With nails keeping them unpolished and dirtying them up with some paint, make up etc works or even chipping already painted nails keeps the messy look alive.
Whatever you do with your hair, whether you wear it down or up in a ponytail matte it up with blood and make it scruffy, you've just been attacked remember?
Shoes, Jewelry & Finishing Touches
Trainers are the best option and, yay, the comfiest! That's all you need for this one, the focus remains on the make up and bloody aspect of the costume. If you cant be doing with using make up to create cuts and bites you can pick some up online for a cheap price.