I agree, you should treat her just as a new member, not as a sibling. We use the supervised methode. The new kid is keep in a seperate room, TV room, the door is open when we are there. It does not take long before every one gets to meet the new kid. With in a cuple of days the door is opened. Yes we have had a few disagreements, but even the ones that have been in the house for years still do.
Just remember that everyone has a differant persnallity.