it depends on what you mean if you FEED Diane to Cici then yes, you are locked out but if after going to Tiffany and telling her about Cici and in the end having to decide to help either Cici or Tiffany if you choose to help Cici then it won't do anything to diane (as long as i know)
while i don't remember how many times exhacly just keep giving her treats untill she asks you for another way.( but i belive it's between 5 and 10 times)
