You certainly handled that well, but that sort of comment is completely unacceptable. You were branded boring simply for the act of not accepting a drink. It's not like she even decided after some time around you that you are boring when sober (which would also be a completely unacceptable remark) but made her comment purely in response to you saying no to a drink. I'm sure you're much more interesting than any of the drinkers she entertains herself with.