Dear Swanky

I guess part of a managers job is to try to have a harmonious and friendly workplace. This is easier if they are open and approachable, which I guess she was towards you and you may have misread or over emphasized the personalization of her demeanor with you. I guess that once she realised that the work relationship had slipped into something more personal from your side that she had to make interactions with you more formal & professional than before.