Once you start using it, don't stop... and constant appraisal while she has it on...
when you go to take it off, don't do it when she is say, scratching at it, or annoyed by it... end with it being a positive situation... (he leaving it alone, when it is not bothering her).
Each time you even just go for a walk, put it on her. That way she gets used to it getting put on and walking with it. And when you get home, is when it comes off.