My daughter is four years old. Have to tell her to sit down and be quiet over 3 times. She thinks discipline is a joke. Could she be autistic?

Unlikely. Try time out for discipline. Get a special bench and have her sit there for 4 minutes(her age). All the best.
Sounds normal. Most kids at that age consider you their servant and find the idea of taking orders from you difficult. They often do much better for strangers. You may need to work with a behaviorist to learn some skills in re-directing her energy and tolerating her frustrating behavior.