Is it ear mites or an ear infection when my cat rubs her ear, over and over, then her leg kind of starts lightly shaking?

Answer 1

The vet will tell you what it is and treat it when you bother to take the cat in

Answer 2

Could be.  Look into the ear and see whether there are scabs or excessive wax.  If so, put in a few drops of mineral oil. Any nontoxic oil will probably work.  Hold the ear shut a few seconds so it drips down inside, then let go.  The cat will rub and shake her head a lot, which is fine because it helps distribute the oil.  This will suffocate the mites.  Add a few drops every day until the ear is clear.