How can i help our resident cats settle with new cat?

[bookwormish]

Just that really.
We have adopted a 4 year old male (unneutered at the moment) but already have a 2 year old female and a 7 year old male (both neutered).
For the first week we started off new-cat in the kitchen and have set up a safe area upstairs for the two resident cats, mainly dd's room. We've allowed new-cat to wander around a bit more when the other two were outside, allowing him venture a bit more into the living room each day. New cat has sprayed once but only in the kitchen and it was cleaned as soon as I found it. I expected issues between the two males but other than some mild growling, they have been mostly okay so-far. Unfortunately our female cat is the one we are having the most issues with! She has gone from a very affectionate cat, to a stressed cat; hissing or growling at everything and hiding. Does anyone have any ideas of what we can do? We've done a sock-exchange, she sniffed it and hissed, then refused to come back into the room. We tried associating introductions with mealtimes and had new-cat visible through the crack of the kitchen door but she runs off and refuses to eat. I hate that we've upset her so much.