I agree with what everyone else has said. I think it's extremely considerate of you to be worried, however I don't see you going out of town the weekend before as being an issue. If I were in that situation I would let my friend know I was going to be out of town and make sure there isn't anything they were expecting from me for that particular weekend. I think at that point there is probably little that you could be doing to help her anyway, the planning phase should pretty much be done.