What kind of wards do players typically buy to prevent evelyn ganks? Is there any that simply detects her? Or can we only ward all her camps as the only option and can only spot her in that area?
Buy 
and ward her camps using your trinket
Normal wards can't see her so you have to use Control wards. Also if the enemy laners start going aggressive for no reason or act weird it's probably because she is either coming or in your lane right outside your sight, so you should pull back.
typically if you ward the area between raptors and red is good and between blue and gromp
that way you can see if she is doing either side of jungle and have an idea of where she possible can go with in a given time frame.
for lane if the tri bush is on your side i would control ward the tri to see if she tries to sneak around and come behind you
