aclimating two older cats to each other again

Question
We had two female cats that coexisted well for about 6 years.  One cat went to the vet for teeth cleaning and when it came home it was like they were strangers.  The cat that was home became very defensive.  She then went away to live with my daughter for a couple of years, came back for a summer and was still very defensive.  She went away with my daughter again but is now back since my daughter is moving and may not be able to have her where she is renting.  So the cat coming back is still very defensive and the other cat who as been here all along is curious but not overtly aggressive or defensive.  We are thinking that maybe she is aggressive in a subtle way we do not see.  So, do you have any advice on how to encourage them to live together peacefully again as they once did?  Thank you for your time, Donna

Answer
Hi Donna,

You need to reintroduce them using a cat intro protocol.

http://www.sdhumane.org/site/DocServer/BT_Cat-Cat_Intros.pdf?docID=621

http://www.sdhumane.org/site/DocServer/Introducing_a_Cat_to_a_New_Territory.pdf?...

These two links will help you. Try using Feliway Comfort Zone. It helps relax them.  Also when you go the vet take all of them. This will prevent them from breaking apart again. Good luck.

Ciao, Karen