Zebstrika's pure Electric-type, just for reference (and so you can perhaps figure out what attacks you should be using on it).
As for Pokemon, I can't say anything much without knowing what your team currently is, but if things really aren't working out for you, she specializes in Electric-types, so Ground-type Pokemon in Route 4 (the desert area) like Sandile might help. Just catch one, and get it to at least Level 29 so it can evolve into Krokorok and you should be good (of course, it's Ground-type moves won't be any good against her Emolga, her Electric flying-squirrel Pokemon, but the main point would be just to have something that's immune to her electric attacks).
But just training and getting your levels up to match the level of her Zebstrika should hopefully be all it takes (again, I can't say anything for sure though without knowing your team). A good spot to get your levels up where you are would be to exit east out of Nimbasa City and keep going until you can get into a little forested area and follow the path to a new place. There will be a Pokemon Breeder right at the entrance of that new area, the Lostlorn Forest, and you can just keep switching between the Lostlorn Forest and Route 16 to battle them as much as you need to get your levels up, which was pretty helpful to me when I got to Nimbasa City playing White 2.