You don't technically have to have a full-time job to emancipate; but few teenagers are going to be able to support themselves with a part-time job. Heck, few adults can manage that.

Also, in states that require you to be capable of self-support, it's okay to live in a context in which you are sharing expenses or not fully supporting yourself, but you have to convince the court that you would be able to support yourself if the situation changed, and that can involve more than proving your current income. In some states you have to have a demonstrated history of self-support, in which case having somebody support you may be disqualifying even if you might be capable, because you're not demonstrating your ability to manage your own finances and support yourself.