D.R.
Make it as fun as possible. Teach her about germs and bubbles, sing a song, get fun soap, fun toys just for when she rides in the car (an example if she wont get in her carseat), etc. My daughter and I sing "Happy Birthday" while she washes her hands to help her scrub long enough." We will name someone who's birthday is close, or, if not, sing "Happy Birthday to Bubbles." Challenging authority is her way of learning what her boundaries and limits are and she will both feel safer and be less oppositional over time if you are consistent. Easy for me to say - I raise my voice to my 3 y/o much more often than I care to!