Aggressive dog won't let me in the house, what do I do?

I did a meet and greet with this dog a couple of days ago, her owner brought her outside with a muzzle - she lunged and tried to bite me on the arm, leg and face. We spent an hour calming her down and bribing her with treats, after that hour she was sweet to me and we went inside the house and she was perfectly behaved. I went to the house to let her out and walk her this morning, she is back to being aggressive, reactive and snarling and lunging. She slams the door closed and growls when I touch the knob. The owner did leave her muzzle on, but I'm afraid. I'm supposed to drop in on her twice a day for six more days while he's out of state.

What do I do????